Knocking sound or vibration coming from bottom of car when driving
 

Cars on coilovers. This sound began after some NASTY pot holes on a road which I don't drive on from now on. Car has been to a very skilled mechanic twice now, who has tightened literally everything suspension-wise, checked under the car, touched everything right down to the battery in the engine bay. The exhaust is not loose at any spot under the car. It sounds like something is knocking at the underside of the car but the mechanic couldn't find it, so here I am seeing if you guys have any ideas as to what it might be. If I missed any details just let me know. Thanks in advance

There was a fellow a few threads back that had a knocking sound under his car that was eluding him. He discovered the front clip (bumper) had become partially detached and was rattling - :iono:


humfrz

Do you have any recordings of the sound?

That was me. It was actually the front grill that got popped loose from the front bumper cover getting caught on a rebar on a concrete wheel stop. I think the grill was beating against the bumper when I was hitting bumps and the bumper was twisting when I was turning. I just pulled on the grill real hard and it popped back into the bumper and the noise went away. Really fortunate that there was no damage and it popped right back into place.

I had some rattling noise from down under before and it turned out to be the catalytic converter breaking apart in my (aftermarket) header. Switched back to stock header to fix.

I'll try to grab a video of the sound this weekend, been running around all week. Keep you posted :)

I'm running stock headers, the sound however is coming from right below the pedals, you can feel it when it knocks the underside of the car.

Yeah, it's not a body issue or rattling issue, it's a knocking vibration... the BEST way to describe it, is imagine your exhaust midpipe was just slightly tapping the underside of the car whenever you went over a bump, you can tell whatever is vibrating is tightened up in other areas, just not the area that's loose.. if you stay tuned on the post I'll try to get a video so you guys can hear the sound.

Those sounds can be deceptive. I wouldn’t rule anything out. Mine sounded like it was under the passanger’s side floorboard or the passenger’s side front wheel well. I had a very reputable tire shop and the dealer check mine out. One couldn’t find anything and the other made the wrong determination.

When does it knock while you are driving it?


(hitting bumps, turning, accelerating, braking, ??)


humfrz

Tighten the top nut on the coilover and/or endlinks.