Author Topic: Mystery Rattle (Read 8359 times)

max123 · « **on:** August 04, 2009, 03:00:53 PM »

This has been driving me nuts for months now. When I'm in 4th or 5th gear and the engine is under load around 3000rpm I get a wicked rattle from the back. No idea what it is. No loose suspension parts, the spare tire is bolted down tight.

Any suggestions? Could it be a loose trunk lid - or something worse?

Cheers

HATER-PROOF · « **Reply #1 on:** August 04, 2009, 10:40:56 PM »

I know what kind of rattle you're talking about, because I have the same noise, but I don't know what is, so when you find out-could you let me know.

DesktopDave · « **Reply #2 on:** August 05, 2009, 07:42:21 AM »

I'd figure it isnt a heat shield, that'd rattle at a fixed rpm regardless of load. The CSB or Diff input bearings would growl dependent on RPM and load. What kind of rattle sound is it? Like a sheet metal rattle or a growling rubbing grinding?

Choking Hazard · « **Reply #3 on:** August 05, 2009, 10:10:05 AM »

I've got it too-
I think it is the tailpipe hitting the valence...

max123 · « **Reply #4 on:** August 05, 2009, 01:11:09 PM »

Nope, not the tailpipe - I just replaced the rear muffler and the noise was there before and after (although that can rattle like a bastard - I had to mount mine a second time to get rid of that noise). Also, not the differential - replaced it with an LSD, and the noise was there before and after. The only two possibilities I haven't ruled out are bad subframe mounts or a worn trunklid gasket. My bet is on the trunklid - I think I may try flipping the gasket around or replacing it to see if that tightens things up.

It could be a heat shield - but that is going to be hard to isolate.

Cheers,

max123 · « **Reply #5 on:** August 10, 2009, 04:18:01 PM »

Not the trunk lid. The lid is easily tightened up with a 15mm wrench - there is an adjuster bolt on the latch which can tighten or loosen the trunk - I tightened mine right down and there was no difference.

I seem to notice the noise from the rear drivers side, so I'm going to get some heat resistant expanding foam or something and make sure the heat shied on the muffler isn't the source of my pain.

BlackBMWs · « **Reply #6 on:** August 10, 2009, 07:55:24 PM »

I noticed a rattle on mine today. Seems to come from the rear underside or shock tower area. New mount on a Bilstien HD. I'll check it out when it cools down a bit. 106 degrees just now... :eek:

Tomorrow, I take the 540it to work... :cool:

HATER-PROOF · « **Reply #7 on:** August 11, 2009, 02:00:46 AM »

BlackBMWs-could you PM me when you find this issue out, because that noise bothers me to the point of embarrassment and pulling over to "punch infant's"(Dane Cook).

BlackBMWs · « **Reply #8 on:** August 11, 2009, 09:16:32 AM »

Sure can. I do know I have broken exhaust hanger muffler straps on the 318ic. These are metal ones around the muffler that the PO had welded on this muffler when the broke. I have two sets of replacement straps. I'll replace the rubber hangers when I grind the metal straps off.

As far as the shock tower area, I'm thinking it could be the new shock mounts themselves, or perhaps worn rear sway bar links.

Perhaps Thursday I can get the car up and me underneath... :cool:

max123 · « **Reply #9 on:** August 23, 2009, 11:55:00 PM »

Fine - be that way. The rattle remains a mystery - thought I had it when I found a few loose bolts on a heat shield - but no.

Everything else is new, has been re-torqued, shaken, lubed - scrutinized...

She'll be rattle'n off into the sunset.

318isfolife · « **Reply #10 on:** August 24, 2009, 07:32:28 AM »

hey check in your trunk by the jack and all that stuff i had a rattle back there to around the same rpm and gears. It ended up being the jack was not tightened down enough and was flopping around hitting up against the wall of my trunk.

Ramblin MAn · « **Reply #11 on:** August 24, 2009, 10:29:07 PM »

It's not a cv joint is it?

BlackBMWs · « **Reply #12 on:** August 25, 2009, 12:56:30 AM »

Update: No loose stuff in trunk. I haven't got underneath for the rattles, but I did notice my sway bar ends on all corners are shot. I'll be replacing those is the next couple of weeks.

I do have something that bumps when I hit one. metal to metal, thought it migh be the vert top as it only does it when the top is up.

Still listening...:cool:

Ramblin MAn · « **Reply #13 on:** August 25, 2009, 07:09:16 AM »

Well, let's put our minds to work. In 4th and 5th under load at 3k, the torque being applied to the drive train is being applied for a longer period of time just because the car is already doing 40. That means the twist applied to all of the components in the drive line will stay twisted longer.

Start with your universal at the diff, then work out. Diff mounts, axels. Get a pry bar and try to move the rear end, and put a pipe wrench on the axel shafts and see how much play you have. Think of the load your engine puts on those parts at 3k in 4th and 5th gear. You can probably be pretty rough

Choking Hazard · « **Reply #14 on:** August 25, 2009, 01:21:18 PM »

I recently read somewhere that E30 rear shock upper mounts can come loose and cause that rattle too. I'm afraid to look...