Engine bay rattle at 3000-4000 rpm

[TaPaKaH]

Hi guys,

I'm new to S65 and have recently been experiencing the following:

Car:
- 2008 M3 E90 Saloon
- 6 MT
- 99000 km (62000 miles)

Issue:
- When under more than 40% (subjective) throttle in higher gears (4th+), a is rattle coming from driver's side of engine bay between 3000 and 4000 RPM
- I did my best to record a video (link) - gradually pulling in 6th gear from 1500 rpm to 4000 rpm. The sound appears at about 18 seconds, or about 2 car lengths before the traffic stop line and stops as soon as I get off throttle. It's much more audible in real life and dominates the engine sound in the cabin.
- Rattle not present when revving engine stationary
- No extra vibration on the chassis or the gear lever
- Rattle not present below 3000 rpm, or above 4000 rpm
- Rattle not present under lower amounts of throttle
- Performance seems fine

Could this be related to the engine's chain guides / tensioners being on the way out and resonating under specific RPM/load? Could it be the variable valve timing (no idea at what RPM does it change on S65).
I'm planning to bring a car to a BMW specialist in the coming days. Was just curious as to what financial damage shall I expect.

Thanks in advance!

[Helmsman]

Can't hear anything in your video but I remember I noticed rattle during the same circumstances when I got my car. Turned out it was the intake filter, believe quite common, I don't even think about it these days.

Edit; believe flutter is the better word for the noise I had. Pronounced at fair throttle between 3-4k rpm, i.e. not metalic rattle.

[Redd]

Also check your exhaust pipes and heat shields. Those are a common source of mysterious rattles, especially since yours occurs around the exhaust resonance rpm.

[Remonster]

I'm currently noticing the exact same thing in my 2008 M3. I noticed it right around the time I replaced my air intake box (put in a new stock one to replace one broken by previous owner or his idiot mechanic) and changed oil from 10w-60 to Redline 5w-50.

I haven't had too much time to figure out what is causing it but I'll post if I do!

[tdott]

What mods have you done or recent work since it started?

[Helmsman]

Get an account make a post never return.

[TaPaKaH]

Thanks for the responses, guys!

I was concerned the issue was engine-related so I put the car off the road until I could have a BMW specialist look at it. Now that I got some assurance that it my be something simpler, I put some 500 km more on the car (including some very easy winter track time) and observed the rattle also at higher RPM (up to 6000) when pushing the car. No error codes have popped up.

Originally Posted by tdott

What mods have you done or recent work since it started?

I just purchased the car and this was the only flaw I noticed during my inspection. Got a good deal so decided to take the risk regardless.

Originally Posted by Helmsman

Get an account make a post never return.

Well, I don't really have much new info to share. All garages are closed for holidays and it's currently too cold and wet for me to get under it myself.

I'll have a BMW specialist (Procar in Zwolle, NL) look at it this Thursday and report back their findings.

[tdott]

Originally Posted by TaPaKaH

T
I just purchased the car and this was the only flaw I noticed during my inspection. Got a good deal so decided to take the risk regardless.
Well, I don't really have much new info to share. All garages are closed for holidays and it's currently too cold and wet for me to get under it myself.

I would start with the basics, put the car on a lift and check for loose heat shields, exhaust, etc. Make sure nothing is loose.

Where you able to confirm if the car was tuned? Hopefully it doesn't have an E85 tune and you are running 91/93? That has happened before when the history of the car isn't known.

Might be a good idea to load a stock 241E tune to start fresh.

[Remonster]

I found the source of my noise and it isn't what anyone wants to hear so I hope the OP is not dealing with the same thing I was.

My #7 rod bearing broke in half and slightly spun. It's a miracle the car was daily driven since my last post late last year until this past week (about 5,000 miles!) with the bearing in that condition but felt fine. In the past few weeks the noise got really loud around 3,500 - 4,500 RPMs under light throttle, a very hard to ignore rattle so I pulled my oil pan and found it.

My shop was able to pinpoint the source of noise with a stethoscope to the middle of the oil pan so if you hear a rattle that is loudest down there, don't wait and end up with a scratched crankshaft like I did.

[tdott]

Originally Posted by Remonster

My shop was able to pinpoint the source of noise with a stethoscope to the middle of the oil pan so if you hear a rattle that is loudest down there, don't wait and end up with a scratched crankshaft like I did.

Any pictures of what the bearings looked like?