M3 Things

[Tyler.M]

Hi kids and kiddies,

I'm part of the "obligatory M3 group" and I have a few questions for you more seasoned with weird German car things.

First and foremost, my engine whistles at idle. Not loud, but enough that you can hear it about 10 to 15 feet away. Belts look pretty new and no cracks, and it disappears under power. Fan maybe? If so, it's time to upgrade to fan-less or go with the diesel fan.

Second, it's making an odd chugging noise at idle too, not necessarily a tick but pretty much a chugging noise. No, I don't think its the vanos as that got replaced around 20k ago. It usually only does this when its hot outside and the car is up to operating temp, so I'm not sure exactly what that means as i'm cartarded.

Third, around 750rpm there's a very weird rattle under the drivers side of the undercarriage. I think it might be the heat shielding, but I can't pin point exactly where it is. Any ideas if heat shielding, if loose, would actually cause an audible rattle?

Putting my flame suit on here, but I've searched around and can't find any definite explanations for this stuff. Since you guys are all lvl. 80 car mechanics, I thought it'd be appropro to ask you.

Sincerely, Obligatory M3 owner.


P.S. Beat a 52 in a 25 mph speeding ticket today in court. Officer said the only reason he didn't give me reckless is because he liked my car. The lesson here, always keep your car nice and shiny. (I don't, I just got lucky that day)

[JustinG]

Vac leak somewhere will cause a whistling and possibly your idle chug. More of a squeal id check any of the pulleys, maybe a bearing in one has gone bad, or is going bad, like an idler pulley.. Also id bet its a heat shield, it may not be loose but possibly bent and hitting the exhaust when the exhaust moves around under acceleration/idle.

[CaptainHenreh]

The lesson here, don't drive like a 'tard. (I don't, I just got lucky that day)

ftfy. :-p

[Jake]

Rattle is probably your exhaust heat shield. If you can, jack it up on four stands and see if anything is loose.

The fans on BMWs are not electric as you know. The fan clutch engages/disengages based on engine RPM and temperature. Are you sure that the noise goes away as you drive? The fan is a pretty audible "woo" type of noise. If it's disappearing under power, I'd guess it's not fan-related. Look for vacuum leaks as Justin said. Start at the air box and follow those hoses at first. There are a few other hoses that are air-related (i.e. not cooling) so poke around at those, too. The good news is, hoses are cheap and easy to replace.

No idea on the chugging. Joey or DJ?

[BLINGMW]

Rattle could also be a loose exhaust clamp, most suspect would be the little do-dad that bolts to the bottom of the transmission and connects to the exhaust. It's always been damaged and/or rusted away in any 3-series I've ever had. It was removed. Or it could be the cat.... just get under there, tap on the exhaust in different places and it should show itself.

[Tyler.M]

It's the heat shielding underneath. Crawled under there when replacing the RSM's (which was a massive fail btw) and discovered a screw had popped out. gonna find the size and get that sucker in there!