Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

6 Cyl 1999 Jeep Grand Cherokee sounds like it's grinding marbles in the engine!


My Jeep started making vague grinding noises from the front of the engine. I’ve tried to isolate the noise using a tube as a stethoscope but haven’t done better than identifying that it’s from the front of the engine. Since the noise started within months of having the belt replaced by a shop my first guess is that they found a way to overtighten the belt and induce some sort of bearing failure (although, I thought that the tension was applied automatically by a spring tensioner). Hopefully the failure is in something cheap, like the belt tensioner or idler.

So, three questions.

1) Can I run the engine without the accessory belt for any length of time? I want to see if any of the accessories are the source of the noise by disconnecting them.

2) Any ideas of other areas to inspect that might make a grinding rattley sound?

3) My alternate guess if the noise is not coming from the accessory belt and what it is connection is that there may be a problem with the timing belt… a loose tensioner.

4) OK I lied… Lord help me, might the main engine bearings make this noise if the accessory belt was overtightened?

Any suggestions will be appreciated. I am trying to do the fishing expedition so that I don’t have to pay a mechanic to. I’ll probably have the repair done professionally if it’s anything more than repairing a belt idler.


I don’t really have a good idea of what the problem could be from your description, but to answer question #1, yes you can run the engine without the accessory belt for a little while. The only real problem is that the water pump and fan won’t be turning so you’ll run into problems with overheating eventually, but if you start out with a cold engine you can run it for a minute or two.

As Greasy Jack said, if you start with a cold engine, you can run it for a couple of minutes with the belts off. If the noise is not there, turn each of the accessories by hand, and anything that feels rough as it turns will be suspect. All these accessories should have smooth bearing action, but some could be hard to turn, like the power steering pump. Don’t forget any idler pulleys.

The “grinding marbles” thing makes me think it might be the catalytic converter coming apart inside. I’ve heard it on several 4.0L Jeeps, and very few others. I know, it’s not near the front of the engine, but sound travels well through metal. Does it change or go away with higher RPM?

1 Like

I don’t notice the frequency of the noise increasing with RPMs. The noise that the car is making is not paticularly loud so it gets drowned out by other noises much above an engine idle. It may be affected by RPM and I just don’t hear it.

So, presuming that it is the catalytic converter failing is this likely to cause engine damage? The car just passed smog. At 95K miles, I am unlikely to pump a significant amount of money into the car to fix the converter if it isn’t doing anything but make noise.

Are you confident that it’s coming from the front of the engine? I think the catalytic converter is usually under the car, not in front of the engine. Confirm if it is the catalytic converter by taking the stethoscope to it.

I just brought my Scion to a shop with the same symptom. They replaced the harmonic damper and the alternator because the vibration damaged it. Since they were taking out old belts, they put in new ones.

And the battery will get drained.

It’s a nine year old vehicle with untold (literally) miles. I’d be reluctant to blame the sound on the installation of the new belt without that being the result of diagnosing it first.

You may have a failing bearing on a peripheral component. Since you had the belt changed at a shop I’m assuming that removing it to check the alternator etc. by turning them by hand is beyond your comfort zone, so I guess I’d just suggest bring it in for them to look at.

Sorry, no disrepsct intended, but there are lots of possibilities for that sort of noise most of them caused by resonant frequencies, and you really need to be there to find it. Hopefully it’ll be just a loose heat shield.

1 Like

Well, yeah, but it’ll overheat a long time before the battery will die.


My reasons for suspecting the work done by this shop is because I have recently discovered that other work that they did on my car was slipshod. The newest work is always the most suspect!

Pulling the accessory belt off to see if the noise goes away seems the most logical first step in diagnosing the problem. If it isn’t an accessory then I guess that I am in for a more extensive fishing expedition than I can do myself. I am open to suggestions as to where else to look.

I can live with a noise. I just want to make sure that I don’t have a catastrophic failure that could have been prevented with a little attention to detail.

As for the untold milage, the car has 95K on it. It’s been regularly serviced. But with tight times, the money is literally going to the squeaky wheel.

Pull the belt and let us know what you find…

So, I pulled the serpentine belt and ran the car. It sounded as it should, no more ?grinding?. This means that the noise is in one of the accessories. I turned each pulley by hand. All felt as if they turned smoothly.

Two exceptions. The belt tension idler wheel was smooth, but there was some sound of ball bearings turning… nothing that sounded like grinding.

The other possible concern was the water pump. All of the other pulleys moved without the ability to move them from their axis of rotation. However, I could lift up a bit on the water pump pulley and it would move a bit from the axis of rotation. Since this would be normally prevented from happening by the tension of the belt I don’t know if this is abnormal.

What now? How do I narrow the problem down to either the pump or the idler wheel?

The other option is to simply run it until something fails outright. Does letting this fail pose a significant danger to the car? I’d loose the belt and have to get towed, but beyond that inconvenience what is the danger? If the water pump fails is there a danger of it damaging the cooling system … bits and bobs floating off into the cooling system (this is presuming that I am smart enough to stop driving before the car overheats).

The last option is for me to replace the water pump. I can follow directions, so armed with a Haynes manual, how hard is it to do this myself?

Thanks for any suggestions.


I’d head to the auto parts store and have them show you some new examples of these parts and see if the wiggle on the water pump or the bearing noise on the idler are normal.

You’re probably generally okay not replacing this, though since either of those should be pretty cheap to replace, I’d do it. If it’s the water pump, another thing that can happen is the bearing overheats and fries the seal resulting in a big leak and the rapid loss of a lot of coolant out of a very hot engine could cause engine damage and will definitely cause an unpleasant mess.

The water pump usually isn’t too hard to replace on a RWD-style vehicle because it’s right up front and after you remove the belt and the fan there’s usually a fair amount of room. You have to drain the coolant, which can be a hassle, and you have to be careful to clean the mating surfaces on the pump and torque the bolts correctly so you don’t get any leaks, but it’s generally not too bad.

The parts store is a great idea! I will check that out and see if I can tell what’s what. I’d prefer that it was the idler, which means that it will be the water pump.

Hey my name is chase but I have a 2000 jeep grand Cherokee and i ran into the same thing, I’m thinking it was the idle pulleybor tensioner and on mine but the sound did shift with the rpms what does that mean? Need help

A problem with anything driven by the belt will shift with rpms, so it could be the idler, or something else. I’d remove the belt and see if anything feels rough, as was done above.