2007 Toyota Yaris, strange knocking

I have a 2007 Toyota Yaris which has run like a Swiss watch for the past seven years, until today. On my way home from work, I was stopped at a traffic light and detected a moderately loud knocking sound coming from the engine. When I got home, I let the engine cool for a few hours, turned it over and the knocking persisted. The sound is coming from the left side of the engine (where the drive belt is located), but definitely sounds like it’s coming from the cylinder head. Turning the compressor on and off makes no difference. This knock does not increase in intensity when the engine is under load or revved, in fact, the engine sounds smooth. Power is as consistent as always too. Never had a warning light over the life of the car and as the sole driver of the car, the engine has never spun over 3500 RPMs.

Only a couple things that have changed recently before hearing this noise:

  1. I refueled the tank yesterday with 87 octane gasoline (using a different pump than usual, if that makes any difference).
  2. It was extremely hot, humid and rainy today.
  3. I changed the oil and air filter myself two weeks ago, as I’ve done regularly the entire life of the car. Oil looks fine and there are no leaks.

In the past, I have noticed light knocking when accelerating up hill or at low RPMs, but I’ve remedied this by filling up with 89 octane or higher. I switched back to 87 octane about a month and a half ago. I’m thinking bad gas might be culprit, but could it be something more serious? I’d appreciate any thoughts!

I tried recording the sound, but the knocking can’t be heard through the audio. I guess the best way to describe it is like a small cast iron pan clacking irregularly on the engine block.


Automatic or manual?

A cracked flexplate (if you have automatic) can make ominous noises.

Check the engine coolant (at the radiator, not just the overfill bottle). If it is low, an air bubble can get into the waterpump and make weird noises. You may have lost some coolant due to the hot weather.

Other than that, there’s so many things that can cause knocking sounds, it’s hard to say. I’ve had a slight clicking sound on my Corolla for the past 8 years. It’s the alternator. I confirmed the source w/a mechanics stethoscope. I just live w/it.

I think the knocking sound you hear when going uphill may be because the plugs need to be changed. Over time the gap increases, and this will cause a ping or knock like sound, esp noticeable when going uphill. Are your spark plugs due for routine maintenance?

What else … hmmm … well, your car is of the age where it might need a new timing belt. Take a look in the owners manual. Is it due for a timing belt replacement?

Has no timing belt. That doesn’t rule out a timing chain noise.

This is an automatic, but it’s definitely not transmission related. I can produce the sound in park or neutral.

Also, listening more carefully I’ve found that it’s still present while driving and the knocking is consistent and frequency, but not pitch, changes with engine speed. It’s definitely on the accessory side of the engine and it doesn’t sound like a valve or timing problem. I thought it was coming from the cylinder head, but I’m not convinced it’s internal of the engine. Does anyone think this could be the water pump or alternator going bad? They are over 7 years old after all.

I’m going to take it to the shop and see what they think. If it is the pump, might as well get the belt and spark plugs replaced too.


So you have an automatic . . .

FYI . . . the flexplate is NOT part of the transmission. It sits between the crankshaft and the torque converter

Food for thought . . .

Sorry, misread that part.

I’ll run the flexplate idea by the mechanic, but isn’t the transmission and flexplate on the right side of the engine? The sound is clearly on the left. I’m very certain of that.

I resolved the problem.

So I jacked up the car to get a closer look at the water pump and found pink residue around the pulley. Cranked the engine, looked underneath while running and the sound is definitely coming from the pump. I’ll get it replaced ASAP.

Thanks for the help!

In my always late non-expert untrained non-mechanic opinion, lower octane fuel could have been ruled out at the beginning. I also have a 2007 Yaris and they (as I believe all Toyotas do) run on regular fuel.

@sjb5001: Thanks for posting back with the solution! All too often people vanish after apparently solving their problems and we never know the end of the story. Like walking out of a theater with 15 minutes of movie left.

Took it to the dealership and they confirmed this. Unfortunately, the coolant that had been leaking from the pump rusted one of the five bolts in place, so the technician had to drop the engine to drill it out to get the old pump off. This was very expensive to do, but I’m happy to say it’s purring like a kitten again.

The takeaway is to inspect your car frequently for things like this. Identifying and addressing issues earlier is always cheaper!



I am having a hard time understanding why the engine had to be dropped (removed?) to drill and extract the bolt.

Perhaps there was insufficient room to use a drill with the engine installed?


The water pump is located snuggly against the engine and right wheel well. With the engine in place, it’s pretty much impossible to get a drill in there. I’m sure this drove the technician nuts because you only need a clearance of 2 inches or so to get to the bolt that was rusted. the service manager said it was his only car for the entire day. Poor guy!


I feel for you AND the mechanic that replaced your water pump!