Rattle from 1,700 to 2,000 RPM

[Logodude]

I have been trying to track down where this rattle is coming from for the past month. It only happens between 1,700 and 2,000 RPM as I'm accelerating (with window cracked/open and less prominent when closed). It sounds like thin metal on metal vibrating. It is very brief but very prominent to my ears. There are no other rattles in the car or at any other RPM band. I have lifted the car and dragged the brakes to load the car and replicate it briefly(I'm aware this is a bad idea but by option are very limited) while someone listened under the car and they claimed it was coming from the muffler area.

The things I have checked with no success:

-Exhaust tips (removed completely)
-Heat shielding around the muffler(removed, inspected all screws, removed any debris, checked for clearances)
-Underbody aero panels(no loose screws or tight clearances)
-Trunk underfloor storage(only the foam insert with flat tire kit)
-Exhaust center support (no loose bolts)
-Brake dust shields (pushed back in case they were touching the brake disks)
-Muffler (has a muffler mod and has a muffler shop cut it open again and inspect for possible causes, none found, had them weld a few areas at my request to eliminate them, and had them weld the tips on)

I believe I missed one major area with the muffler. If I'm not mistaken, the muffler has a double wall on the outside. Correct me if I'm wrong, but I think this could be the cause but I'd have to cut it open again to check this.

Are there any more area I need to check? I feel like I have hit a dead end on this matter.

[Thik]

Ive had a rattle between 1,700 and 2,000rpm since I've got the car 70k miles ago. Sounds like a metal shield coming loose or something. Car has been fine for all those miles. I attribute it to one of many random quirks the M3 has that gives it character.

[Logodude]

Originally Posted by Thik

Ive had a rattle between 1,700 and 2,000rpm since I've got the car 70k miles ago. Sounds like a metal shield coming loose or something. Car has been fine for all those miles. I attribute it to one of many random quirks the M3 has that gives it character.

This issue started about 2 months ago, which make me think it is fixable. I don’t believe it’s a “problem” but it very annoying and I don’t like it at all.

[ItsGary]

Does the rattle sound like anything you'll hear in this video?

If so, I think its the Throttle Actuator Gears. The only way for me to find out is by replacing my TAs (Still on original ones with 127k KMs)

[fatalelement]

Originally Posted by ItsGary

Does the rattle sound like anything you'll hear in this video?

If so, I think its the Throttle Actuator Gears. The only way for me to find out is by replacing my TAs (Still on original ones with 127k KMs)

I have a similar rattle and both my throttle actuators are brand new from BMW as of a week ago, so I'm willing to bet that's probably not it. I've had mine since I got the car, everything seems fine despite it.

[Logodude]

I have noticed when accelerating moderately hard to full throttle, the noise will go away for a short period of time. To me, this reinforces my theory of the muffler wall being the cause of the noise. Unfortunately, a lot of places are closed for the weekend. More to come with time. I should have an update next week.

[StripclubDJ]

Bang your hand on the exhaust from the cats on down
Make sure the heat shields by the o2 sensors aren't pushed against them

I've seen some nasty rattles from the heat shields above the primary o2 sensors

[Logodude]

[m3jala]

Sound anything like this? For me it was prominent during cooler temperatures and relative to speed not rpm. Most noticeable around 40mph and sounded like it was coming from the gear box. In my case it was the heatshield rattling against the drive shaft after a bad exhaust job at the dealer.