Car makes loud banging/grinding noise only during heavy downpour rains

I have a 2000 Toyota Camry LE with 106K miles. It?s getting a little clunky but works perfectly. I do regular maintenance like oil changes every 3 or 4 months, breaks, tires. Last year one day during very have down pour rain I noticed something banging/hitting under the seats while driving in this heavy rain & car losing power (slowing down). Something (I am guessing the exhaust pipe? hitting the body. The more gas I gave to gain speed the violent the banging. I slowed down to almost 15MPH but never stop & the car started to work normal. It happened 3 or 4 times before I got home. I check all fluids etc? All normal. Drove later in sunny, cloudy & even in light rain the car runs perfectly fine. Then it happened again in heavy rain. I told my car mechanic & he checked all even tightened the main belts (not timing belt). No change. Now it?s so predictable when ever its rains heavy & even slushy snow/rain. Lately it started to not only lose power but sometime instead of banging I hear grinding noise when pressing the gas paddle. Some time banging followed by grinding but every time after slowing down the car recoups power and I drive normally. It never ever happens in dry day. My wife who drives ?Buick Century 2004? thinks my car is dyeing and should buy a new. When I describe this situation to any mechanic they points to transmission & want to perform brain surgery to diagnose. I love the car but don?t want to pay for trial/error fixes. Would anyone know what?s wrong & cost to fix?

This might sound a little crazy, but have someone check your inner fender liners and front shroud. Water will hit these with a lot more force than just air and could possibly distort one of them enough to hit one of your tires.

The shroud and fender liners are made of plastic and for the most part, held in with those push in plastic fasteners. If one or two of those fasteners break, the panel can distort, but when up on the lift, it will be in place.

In 35 years I have had many, many reports of cars running in a way other than the way they are designed to run related to the weather. I cannot remember one where the customers description that “it only does it when it is raining” has been supported by a resolution of the complaint. In short,I believe your car has a problem but it is not related to the rain. These reports get so specific that I have heard stuff like,“it happens only when my son is in the front seat and my daughter sits behind me and not my son”. As mechanics we have to sort out why these people are linking these conditions with these symptons.

You both maybe correct. Oldschool: I know there is a problem & that?s the reason I need an ?expert? like you to help narrow it down. I can demonstrate the problem every time in ?heavy downpour? though but can?t create heavy downpour on demand for the mechanic to see. I hope you understand what I mean. Is there any link between a lot of water wetting the engine belts, transmission while driving above 40MPH to cause something (belt/gear) to slips that cases engine to act all crazy (shaky) and consequently exhaust pipe shaking violently? I am a Network engineer & not a car mechanic savvy but understand that concept. Unless it?s happening all the time when dry unnoticeable & heavy wet weather just amplifies the symptoms? Just an FYI: I never had or needed any major repair, all original including the drive belts. The mechanic who tightens the belts says all belts are perfectly fine but hears a ticking noise. Timing belt or the tensioner or something hitting the casing wall. He advised replacing timing belt and all including water pump for $375 but would not guarantees the fix.

The timing belt isn’t making a banging noise under the car.

How fast are you going when this noise occurs?

I have been thinking about this one b/c it is so odd. And I think that keith has really hit the only thing that makes any reasonable sense. I will just add that one thing to take into account is that your tires are designed to channel water away from them - and most of that out the back. So imagine turning on your garden hose and blasting it at a loose, hard piece of plastic in the vicinity of both the car body and tire (i.e. your fender liner). I think that banging is perfectly plausible. The grinding will either be from a rapid vibration and/or it being pushed to rub on the tire.

I’m feeling good about that WAG. Perhaps you should pull out the garden hose or get to a car wash power washer & do some experimentation.

Normal highway driving speed (55-40MPH)?. It never happens on the local stop/go streets even with downpour, only on HWYS while moving, occasionally & only on heavy rain day. Sometime when it happans I have to slow down to almost 20 or 15 for the car to gain back control/power until it happens again. Everyone points the ?grinding noise? to the transmission but knocking happens first then comes the grinding unless I slowdown before grinding occurs. Sometime when grinding happening I will remove my foot off of the gas & let the car cruise & tap gas just to make sure if the grinding is still there or gone. I resume normal speed as soon as I feel no grinding or knocking. I cannot recreate this on a dry even light raining day.

It happened again this morning while going over the Throgsneck Bridge, NY & it?s was raining hard too. Keith: Last night I checked both fender liners with a flash light & didn?t see any thing wrong with it. I will recheck this weekend in day time. Very puzzled! BTW, last summer 2010 I replaced/balanced/aligned all 4 tires (all season) from Mavis. I also changed the spark plugs only. Pressured water hitting the fender doesn?t explain losing power though. To me its feels like engine suddenly running on 2 cylinders which shakes the whole engine that shakes exhaust system that?s hitting the undercarriage? but cant understand why it doesn?t happens when dry or after slowing down the car drives normal?. (Scratching head) I truly appreciate the advise.

Any chance this could be caused by water being thrown up on the accessory pulleys and (if belt and tensioners are not in great shape) the problem could be a belt hopping badly on the pulleys?

I’ll think about this some more so I’m just throwing that WAG out there for now as something for consideration.
As weird as it is, most of the these types of things come down to something so simple that one often sits back later and wonders why it did not hit them right off the bat.

This changes things, a lot. The reason for loosing power for water hitting the inner liner would be that the inner liner is loose and it hitting the tire. The extra drag is where the power loss comes from. I have seen this once, but now I am convinced the problem is with your spark plugs or spark plug wires.

Heavy rain is getting the wires wet and they are arcing to a nearby ground or the wires are not firmly seated on the spark plugs and they are arcing from the top of the plug to the head. Simply press down firmly on the boots and see if any of them click into place.

If any feel loose, but won’t click into place, go to a parts place and get some dielectric grease. Put a little grease on the inside of the rubber boot, just enough to coat the inside up to the contact. Use a small coffee stirrer or nail to spread the grease. Then put them back on. Do only one at a time if you are not familiar with the firing order.

If the 2000 Camry went to coil on plug, then this will be more difficult. You may need to take it into a shop, or back to Mavis and have them check for you, they may not have secured a coil properly. If you can see the coils, they may have left the engine cover off.

Thank you all for pointing me to the right direction! I will check plugs/cables this weekend & post prognosis? I want to keep the car, should I spend money to replace all belts including timing belt & water pump? I truly appreciate the help.

You should be able to find out pretty quickly about the plug wires and such without much ado. First, pick a time that you can make it really dark and just watch under the hood while the engine runs. Look for any signs of a “light show.” If you see nothing start misting things with a water bottle to see if you can make the engine do anything funny.

You should check your maintenance schedule in your owners manual. If you have a timing belt instead of a chain, then I think the interval was 4 years/60k miles so if you have followed the schedule, you won’t be due until next year. If the serpentine belt looks bad, then replace it, otherwise, just consult with the owners manual.

So you do not feel alone, I have the exact same problem with my Camry LE. It is a 1999 with about 95K miles on it. Had no problems until about 6 months ago when our area received a heavy rain. i.e. 8 inches or so in a few hours. While driving home in the rain (and large puddles), I heard this banging sound coming from what sounded like underneath the floorboard. I slowed down, the banging stopped and did not start again. Since then, and in two seperate heavy rains, same thing happened. Only at higher speeds and only while raining. To me, it seemed like something to do with the muffler system but of course, sounds in a moving car can be deceiving. Wierd. Let me know if you or anyone else knows the fix to this.

Problem fixed: I took the car to a very knowledgeable mechanic who mainly restore old cars. I described him what?s going on & he immediately knew it! Bad spark plugs or cables. I had him change the water pump, timing belt, fuel filter & a complete tune-up (new plugs & wires). He also found some minor leakage on the ?cam shaft? (?) & fixed it. He did find two cracked plugs boots & thinks water was causing it to fail, the car runs on two cylinders, the whole engine shakes crazy and the resonance travels to the hanging exhaust pipe causing it hitting the underbody. Total cost $500 even. The car also got little umps. Case closed! Keith you win!

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Hi bro … My car have same problem too when heavy rain…how to settle the problem … only change spark plugs?pls help .