Hi guys,

A few days ago my 2005 MCS has developed a knocking sound whenever I brake and accelerate at around 30km/h. After reading so many threads on motor mount failures, I brought the car in. After a short diagnosis, the dealer agreed the motor mount was bad so they replaced it under warranty.

HOWEVER, the sound is still there! It almost feels like this is weight-transfer related, because I can make it knock as many times as I want if I get it at the right speed and then hit the brakes (it knocks), accelerate (it knocks again), brake (and again)....

I'm bringing the car in again next week, but I'd just like to see if anyone here has encountered a similar problem before and could shed some light...

I was planning to install my new coilovers too this coming Monday

 

Anyone?

 

It could be the lower control arm bushing going bad. This is on the rearward end of the control arm where it attaches to the subframe. Unlike the forward end which has a ball joint, the aft bushing is a rubber affair that is prone to failing. The fore-and-aft pressure on the lower control arm when accelerating/braking will cause the control arm to clunk around inside the bushing body if it has failed. It's worth a look.

Other sources of a similar noise under those circumstances are the lower engine reaction brace (goes between the oil pan on the pulley end of the engine to the subframe, it's use to control engine torque reaction), exhaust hangers (the forward one most likely, noise caused by the exhaust moving with the engine torque reaction), driveshafts and struts.

 

Thanks Greatbear. I found the culprit!
The bolt holding down the swaybar bushing was coming loose! torqued it down again and the noise was gone...I really thought it was something more serious than that. phew!

 

Glad it was nothing serious, and you caught it in time.

 

Ohh, any chance someone can describe (or post a picture of) where these swaybar bolts are at? Do I need to take the tires off to get to them or anything? I know next to nothing about the mechanics of the car but I'm pretty sure I can check for loose bolts.

My 2005 MCS is doing this exact same thing. Just started. I accelerate, something goes 'knock', I let off the gas, something goes 'knock'. I can make it happen almost at will. I just need to take an action that makes the car rock forward or back the right amount and I'll get my little 'knock' sound. I can't tell exactly where it's coming from but I'm almost positive it's not coming from the engine compartment -- sounds more like an undercarriage thing. I came here searching because I wasn't even sure what to bring it to a mechanic and say about it (and the nearest MINI dealer is quite a drive).

(From the sound, my first thought was just that there was something rolling around in the passenger compartment! It's just a little metal-on-metal tap like something loose flapping back and forth.)

 

I have MCS 05 and was experiencing that knocking noise as well. Everytime I accelerated and stopped just like you said. I just took it in and they told me the same thing...motor mount. Had it replaced and drove it home with out any noises. (so far)