The rear end is rattlin' like a tin can full of rocks.....

[Klug]

So my trusty dirty30 took a time out today. I've put over 200miles on her over the past two days and had no problems whatsoever. Today mid-day I started to hear this "Tin can full of rocks" rattle coming from the rear end. Odd behavior since I only get this noise when I am off the throttle and the car is rolling in gear. Clutch in/Accelerating/Rolling in Neutral and Shifting, the sound does not happen.

So I jacked the rear end up, hoped in and started it up, tranny shifts fine and no noise getting up to 3rd gear. So this only happens when the car is rolling in gear and off the throttle.

At first I thought it was a bad wheel bearing, since I've been hearing clicking in the rear, however that still doesn't make sense since I don't get the sound all the time. For kits n giggles I took the wheels/calipers off and I don't have any play in the hub or hear anything out of the usual.

What do you think I have going on here? Diff? Busted CV? Maybe the catalytic converter broke and its rattling from the back pressure? I'm just curious for what I should look into, the car is 2h away at a friends house and want to get my thoughts straight before I take the weekend off and rip the thing apart. Any advice is appreciated! :)

Take a listen for yourself
http://www.youtube.com/watch?v=ux0eZIK5o5k

[Cronopoulos]

Does the noise effect the way the car drives? Around corners?

[Klug]

Nope, it rides perfectly fine even around corners :/

[Smelser]

Try checking ALL tin heatshields everywhere. It sounds TOO "tinee" like tin metal to be a major gear or bearing issue.
JM.02$

[jlevie]

I suspect that the rear suspension is shifting under deceleration and the drive shaft is rubbing on a heat shield. Bad subframe and/or diff bushings could do that.

[gp.plus]

I would have to agree that it sounds like something hitting a heat shield, in addition to what's been mentioned above, check the csb and guibo as well. On a side note I would be extremely careful taking a car up to third gear speeds on jack stands, could get ugly real quick.

[Klug]

I'll investigate all the heat shields first, It does sound like something is rubbing but how is it possible to only be rubbing the drive shaft only during deceleration?

If thats not the trick on to the rest of the suggestions. I appreciate all the input, I really hope its going to be something easy(-er)

[CHIF8008]

thorough inspection of the underside for "shiny" edges or worn grooves will tell what was rubbing or rattling. deff. sounds like something is loose/ broken mount for exhaust or the heat shielding.


should be a easy fix. i had the one back bolt for the heat shield come off and it barely would rattle on the driveshaft. i thought something was really wrong but i was able to zip tie it up and have not have a problem since

[gp.plus]

I'll investigate all the heat shields first, It does sound like something is rubbing but how is it possible to only be rubbing the drive shaft only during deceleration?

I would think there are different types of stress placed on the drivetrain wether you are on accel or decel, that being said my guess would be that the drivetrain is moving as opposed to the heat shield moving to rub the DT.

[jlevie]

I'll investigate all the heat shields first, It does sound like something is rubbing but how is it possible to only be rubbing the drive shaft only during deceleration?

When accelerating the subframe is pushing forward, relative to the car body. But decelerating the subframe is pushing back relative to the car. Ordinarily the subframe doesn't really move, but if the subframe bushings are bad it can move. Because it has a three point connection to the car with the third point (the differential bushing) aft of the other two points (the subframe bushings) deceleration forces can cause the subframe to rock, lowering the front of the subframe. That would cause the back end of the drive shaft to move down, which could bring it into contact with the heat shield.

[Klug]

Any chance it can be the catalytic converter rattling around? Granted I should hear it from the mid vs. the rear. If this was the case shouldn't it rattle under load and idle also?

[Klug]

Wow. Found my problem.....



How the heck do TWO of these bolts get loose and come off? especially from the top! I had to drop my rear a few months back when lowering the car. I did have a highly recommended BMW shop do it....crazy.

So now i'm in need of these two bolts...any one know what size these might be? Should I use loctite?

[Mr. Tasty]

fuck... lol

[Klug]

Ran to Lowes (Probably not the best automotive bolt supplier) and picked up two ones that fit perfectly. Everything is all better now.

I'm still in shock about it all...First off HOW? Secondly, if they were removed by the shop to put springs in, how did I put on over 500miles like this?

[gp.plus]

Wow. That's crazy, take a good look at your diff bushing, it has most likely been taking a beating.

Not sure why they removed those bolts to put in springs.