So I have a new mystery (at least to me) on my hands. Yesterday on the way home, I noticed a slight thumping/clunking sound coming from the driver side while going slowly in the neighborhood. It sounded like a tire had picked up a rock or screw as the speed of the sound was timed to the tire rotation and the nature of the sound seemed like it was coming from the tire/wheel, like when you go over a road marker but much softer. I did not feel anything in the ride of the car, brake pedal or the steering wheel when the sound occurred. But the sound went away after making a turn so I thought the rock had come out. This morning I noticed the sound again, and before it went away I was able to listen more closely. It appeared to come from the rear tire on the driver side. So I did a visual inspection of the tire tread and wheel well (+1 mode helps with that) – thankfully there were no screws or nails, only pebbles which I removed. I also did this with the other three tires finding nothing but pebbles.

However, after removal of the pebbles, I headed to the office and noticed that the sound would come and go while driving despite removing those pebbles. And since it would come and go I figured it could not be something stuck in the tread as that would be continuous. During my short drive in, I did not notice the sound while accelerating or braking. I did notice it while coasting. However, if I touched the brakes slightly the sound went away. For example, I made a right turn and sped up to 25-30mph without hearing the sound, but when I let off the gas to coast to my next turn the sound could be heard at a rapid pace. As the car naturally slowed, the sound timing slowed also. Then I tapped the brakes for a moment to slow down more, and the sound did not occur while coasting after the brake tap. Then after the next turn I noticed the sound again during coasting. Again there is no feedback in the ride, steering wheel or brake pedal.

Thinking back to last night and this morning, I was probably also coasting (covering the gas or brake pedal but not applying any pressure) in the neighborhood when I heard the sound before. This is a new one for me – never had a sound come and go like this.

Next I plan to check the lug bolts and brake pads on the driver side. Any other ideas?

 

Hey Fisch, Maybe you have a sticking piston in your rear caliper that isn't retracting properly. When you tap the brake pedal it may free it up for a while until it extends and sticks again, pushing on the brake pad. When did you last replace your brake fluid?

 

Yeah, when I tapped the brakes and didn't hear it after I thought that was odd. I really need to drive it more to evaluate the symptoms. Brake fluid was supposedly done during last service about 8 months ago. Haven't had a sticking piston before. How do you diagnose that? Would that make a constant sound while it is sticking or one that is timed to the tire/rotor rotation?

 

It would be a dragging sound that could come and go if the rotor was warped, or more of a consistent soft grind noise.

 

Check your CV joints.

 

I know that on most cars when the brake pad gets worn there is a clip that starts to wear on the caliber. That would cause a clicking noise that would come and go

 

Thanks everyone for the ideas. Well on my drive home I heard nothing at all. I tried all kinds of scenarios with lot's of coasting, light and heavy braking, etc. For a few stretches, I even had the climate, radio and seat vent fans off to reduce competing sounds (made for a boring, warm ride home). The sound was very clear this morning. Perhaps it will return tomorrow or remain a mystery.

Will have to wait on that until I get the time.

This was a different sound than that. But I will check the caliper movement once I can get someone to help me test drive it.

The pad thickness looked good. At the last service 8 months ago, they were half-worn IIRC.

I did get a chance to check the lug bolts. I wasn't bearing down on them, but none of them budged except for the front passenger tire. On that one, most of them moved very slightly (less than a quarter turn) before the car would rock. I don't have a torque wrench so I couldn't be exact but in my experience, they seem tight enough.

 

There is only one pad sensor on your car in the front and back and it has a long peg that will wear and cause the warning to pop up. I doubt that is the cause of your noise.