What is this mystery noise?

[ewrjontan]

So after replacing my clutch, all of my bushings/mounts and my old coilovers for some ground controls (hybrid setup) I finally have the car driving. I have been driving the car for a couple of weeks and I have a mystery sound: it sounds like I have a bunch of those rubber chickens in the center of the vehicle.

Similar to this...



I will try and grab a video tomorrow but here are some noticeable features:

The sound occurs:

• Only when moving (very slow speeds to 30-40 mph; by the time I hit highway speeds it either is gone or I just can't hear it)
• with clutch pedal in or out; happens when in gear or coasting in neutral
• with brake pedal in or out; happens regardless
• regardless of pavement smoothness or mid turn/straightaway.
• intermittenly; it seems to start up after about a minute or so of driving...then comes and goes at random times.
• regardless of speed; does not sound any different at 5 mph vs 15 mph. Then again, highway speeds I can't hear anything so who knows

When I first got the vehicle driving, I noticed that my rear passenger side brake pad anti-rattle clip was missing. Bought a new one and unfortunately did not fix the issue. It's so difficult to diagnose since it is intermittent; if it happens, I try to hold it in the same speed and gear but then it goes away and can't repeat it. It seems totally random.

I figured maybe it is my driveshaft center support bearing but that is brand new (and a genuine bmw part) and it's been like this since the day it was installed. The driveshaft/bearing was preloaded as well prior to tightening the bolts. Keep in mind, my engine is sitting a little higher (like a 1/4 inch if that) due to my subframe-motor-mount reinforcements so maybe I need to adjust the preload?

It seems to be coming/felt from the center/center-rear of the car. I can feel the vibrations in my parking brake however, everything spins freely and is properly adjusted. If I pull up on the brake while moving, the sound does not change. I am assuming it is tranny or driveline related.


Any thoughts? It is a mystery and I am afraid that something is just going to blow up once I get it on the track...I really don't believe it is a bushing issue.

[hc1001]

Guibo, driveshaft bearing, insulation hitting something under the chassis?

Have you gone under the car yet? that would be the first step.