[jackolinu]

So, I've had this noise and it's driving me crazy. It started about a year ago but it's getting worse. It's a knocking or rumbling noise from the front, heard from the footwell area, that happens every time I brake, especially on a rough surface. Things I changed so far: shocks,top mounts, tie rods, steering rack( I had some free play so thought might as well), discs and pads, caliper bolts, stabilizer bar including bushes, stabilizer links and lower and upper control arm bushings. Only thing I know of that I haven't changed are the control arms, which include the ball joint. I have no clue as to what it might be and my mechanic is as baffled as I am, because he can find nothing lose. I'm now thinking of changing the control arms, but my mechanic is sceptical about it, he said it doesn't sound like the noise of a control arm. Any ideas?!!

 

[muris93]

Hi,
once i had a similar issue, in my case at different times usually when the car was at low RPM, accelerating something was rumbling below me.
It turned out to be that my central exhaust holder was missing, probably got disconnected and fell out at one point although it's still a mystery how this happened because the piece is not small. This rumbling was happening because nothing was basically holding the exhaust pipe and it was hitting the sides of the floor.

In my car, it's an L shaped part which gets connected to the transmission box i believe. That part also has something like "distancer" which allows the exhaust pipe to freely move left and right to some degree not allowing too much movement.

Did you check engine mounts? Those are pretty much hidden from the eye, maybe these are at the end of life so the engine is producing the noise upon braking?

 

[jackolinu]

Thanks for your reply. Engine mounts and gearbox mount are also new! Will have to check the exhaust brackets and see that nothing is lose. My mechanic is also suspecting it could be the steering rack, even though I replaced it, but I didn't buy it new, it was a refurb, so he's thinking the bearings inside weren't changes and it could be the culprit! I have to take the car at him next week and leave it there so that he could take out the rack and check it thoroughly. Hopefully he'll find what it is that's causing this annoying knocking/rumbling everytime I brake!

 

[muris93]

Alright, i found the part that i had to replace/add if you might look for it.
The thing attaches to the exhaust pipe and to the gearbox.

To be honest, i doubt it that steering rack is causing the noise, but again it depends what kind of noise do you hear. Another thing, some mechanics would eagerly want to squeeze $€ from you especially when it comes to MB cars. So i will suggest seeking another opinion from other mechanics just to be sure.

I don't want to diminish the value of anyone but i had my own dose of BAD experience where one says this and another says that, while in reality solution is a cheap replacement part / fix.

 

[jackolinu]

Wow ok, didn't even know our cars had that!! I will definitely look out for it next time it's on the jack!! Yesi know what you mean about mechanics, I had my fair share of experiences where they try to guess what's wrong whilst you for out the money for parts!!

 

[muris93]

Wow ok, didn't even know our cars had that!! I will definitely look out for it next time it's on the jack!! Yesi know what you mean about mechanics, I had my fair share of experiences where they try to guess what's wrong whilst you for out the money for parts!!

Yep, mine was missing it totally but exhaust pipe has mounting points so if it's not there mounted on yours it means you are missing it.

 

[Benzyle]

Mine had one of those bolts missing...worth checking them for tightness and or removing and replacing with some thread locker applied.

 

[jackolinu]

Mine had one of those bolts missing...worth checking them for tightness and or removing and replacing with some thread locker applied.

I have an appointment with my mechanic next week and already told him to check all the exhaust brackets when it's on the jack. Thanks for the heads up!