AG94

Hi everyone,

I've been getting this noise from the front of my car while driving. It is a dull rythmic thumping sound that varies in frequency with the speed of the car. It gets greater in intensity at high speeds but is noticeable at speeds as low as 10-20 mph. It is a sound but also a feeling that can be noticed through touching the seat, floor, etc. a mechanic took my car out for a ride and told me my front left wheel bearing had gone bad and he replaced it. The sound is still here and the same as it was. I also hear the sound while coasting in neutral as I read that this can rule out a drivetrain issue. I just had my road paved so it is completely smooth and I had a chance to drive the car while looking at the front passenger wheel out the window. It seemed as if the tire was moving up and down like it would if you were riding over a bump, but on a completely flat surface. I swapped the tire out with my spare and tested the car only to hear the same noise. I have no idea what this could be. I was leaning it towards being a flat spot on the tire due to the sound and movement of the tire, but the sound was reproduced with the spare. A little while back I did have to stop short on the highway causing me to skid with some burnt rubber. Anyone have any ideas?

John535is

You need to check the suspension control arm bushes and the strut mounts.
My guess is the top strut mount. I say this because it would provide the problem you experience and, assuming your mechanic who replaced the wheel bearing actually looked at the control arm bushes, and checked the strut (shock absorber) the one bush you cannot really see until you remove it is the top one. The top of the shock absorber is connected though the centre of the bush. What can happen (this happened to me) is the centre of the bush completely tore away, so the top of the shock absorber was bouncing around. The good news is that they are relatively cheap, the bad news is that you cannot really see the bush until you pull it out, so difficult to say for certain until you spend the time to remove the old one. If you want to picture the bush. look up part number 4D0412377F.

AG94

Thanks I'll give that a look. I had a mechanic replace both of the axel assemblies in the front last month (the noise was there before hand).. Would they have been able to see that while in there?

AG94

Also is it likely for a bad bushing to cause this constant ryhthmic sound even when driving on a flat surface where the suspension isn't taking as much of a load as it would be going over a bump?

Prospeeder

To me it sounds something like wheel bearing, axle, transmission's differential, or tires. I cant say I have seen torn control arm bushing cause that kind of noise, usually just clattering over bumps and rough roads.

AG94

I've looked at the tires and couldn't see anything visually wrong with them plus the sound was still there after swapping with a spare. I recently had both front axle assemblies and control arm bolts replaced as well as the front left bearing. So maybe it's differential but I read that if the noise is there while coasting at neutral then a differential issue can be ruled out. Any possibility a warped rotor could cause this noise even while not breaking?

John535is

You wrote about "the tire was moving up and down like it would if you were riding over a bump, but on a completely flat surface" which still points to a bush problem. Warped rotors are uncommon these days. (not impossible) but would not cause the bounce movement anyway. If you have done the axle assemblies, that should rule out a bad CV and you have done the bearing. Assuming if you had the control arm bolts replaced (why?, and did they use the correct size when replacing them) then whoever did that presumably would have checked the control arm bushes at the same time. And as Prospeeder advised, that normally produces a clattering type noise. So that leaves the shock or strut mounts. The bottom one you can see from the wheel well. My money is still on the top bush because I had a similar experience. I used to notice it more on flat surfaces because the other tire and suspension noise is quiet and I would get this annoying thumping over seemingly flat road. Anyway, the bush is like a thick donut, the centre has a metal sleeve bonded into it that the top of the shock absorber is fixed to. Mine had torn most of the metal sleeve away from the bond just enough for the top of the shock to touch the metal mounting. Interestingly, just trying to bounce the corner wasn't enough for the strut to hit the mount and because the strut or shock was Ok the problem was not apparent. If you are OK with tools this is not a big task just time to disassemble the strut, the part is cheap. ($10 for aftermarket, $50 genuine each). If you check on-line suppliers like ECS they have kits with new bolts and bits, (I'm sure other do too).

AG94

Thanks for the info. It's currently at the mechanic being checked out so I'll bring that up to him. Ive done some simple repairs on my car in the past but am much more comfortable having a mechanic handle it. I forget why the control arm bolts were replaced but I remeber they said something about them being frozen on and breaking when trying to get them off. When I find a solution to the issue I'll post back.

AG94

Update.. My struts are infact going bad, which caused my tires to feather which is causing the thumping noise. My mechanic rotated the tires and the noise moved to the back of the car. The tires themselves still have very good treads and replacing the struts would not cure the noise until the tires were also replaced. The mechanic did not seem concerned about this being an urgent fix (and knows I've already put a lot of money into an old car) and said it would not be an issue to wait to do the struts until the tire

AG94

Update.. My struts are infact going bad, which caused my tires to feather which is causing the thumping noise. My mechanic rotated the tires and the noise moved to the back of the car. The tires themselves still have very good treads and replacing the struts would not cure the noise until the tires were also replaced. The mechanic did not seem concerned about this being an urgent fix (and knows I've already put a lot of money into an old car) and said it would not be an issue to wait to do the struts until the tires need replacement as long as I can tolerate the annoying noise. Let me know what you guys think