How to diagnosis source of rattle

[Avusbluem3]

I have this rattle coming from the engine that I hope you guys can give me some ideas on how to diagnosis.
It can only be heard while driving with the engine under load between 2 and 3k rpm. It cannot be heard while idling or reving in neutral.
It's so faint that if i crack the windows a bit to see if it can be heard from outside, the wind noise drowns it out.
Obviously if I had a dyno, I can strap it down, put it under load and listen from the engine bay.
I've checked the engine and under the car for any metal to metal contact.
Any tips, techniques, tools that can help me find the source?
Thanks.

[Cubieman]

You could jack up the rear and have a buddy drive it while you probe around for the source of your noise. But if you do that be very careful and take all necessary safety precautions!

[FBloggs]

I would cut useage and would advise you to get the rod bearings checked asap. Is the noise at crank speed or is it at cam speed?
Try a stethoscope.
The other possibility would be preignition if you happen to be lugging the engine...
Have a butchers at the front accessory drive pulley arrangement. See if a pulley is rocking .

[Avusbluem3]

You could jack up the rear and have a buddy drive it while you probe around for the source of your noise. But if you do that be very careful and take all necessary safety precautions!

Thanks for the suggestion. I tried that but because it's only heard under load, I was not able to replicate the noise.

[Avusbluem3]

I would cut useage and would advise you to get the rod bearings checked asap. Is the noise at crank speed or is it at cam speed?
Try a stethoscope.
The other possibility would be preignition if you happen to be lugging the engine...
Have a butchers at the front accessory drive pulley arrangement. See if a pulley is rocking .

Thanks also. Rod bearings were replaced around 20k miles under recall and I currently have 66k so it should not be the bearings (I hope).
Not sure how to determine crank speed vs cam speed from within the car.
I've seen may tips on using stethoscope to help pinpoint a noise but again it does not happen at idle or just reving in neural.
I've replaced all the idler pullies. Can a bad water pump have these symptoms?

[Arith2]

Do you have headers?

[Avusbluem3]

Do you have headers?

Yes I do. I've check that it's not touching the engine mounts. There's actually a good half inch clearance so even after the headers heat up, they should not touch. I have the stock heat shield back as well which I've elongates the bolt holes so I can have them higher so they do not touch the headers.

[Arith2]

My headers caused alot of crap to rattle compared to stock. There's just rattling at those rpms. Even bone stock there is a little. Post a video just to be safe I'm talking about what you're asking about but it's possibly normal.
My car has headers and a loud exhaust, and it sound embarrassing at those ranges. It's rattles ALOT

[FBloggs]

Arith reminded me of exhaust manifold leakage at the head flange,lambda sensor or the next flange. ie, a leak near the head. This can sound like a rattle.
check for a loose spark plug, while you hunt the problem.
The m/s52 waterpump that fails at the bearing does tick in my experience, once it has spit out a ball or 2.
Don't know if this applies to the s54 but sometimes there is no coolant leakage either.
only occuring under load is a little ominous. Maybe a blackstone oil analysis.
Try to avoid driving it until you know what's going on.

[Halftim3]

There was a thread on the old m3forum with photos of the chain rattling/hitting the oil pump tube, that would be my guess.

[Rajvosa]

i had pinging between 2000-3000rpm and head gasket was the culprit. maybe check compression...

not my video but my noise was same... https://www.youtube.com/watch?v=b1gCbcS0IMU

[Cubieman]

Thanks for the suggestion. I tried that but because it's only heard under load, I was not able to replicate the noise.

If you partially engage the parking brake while driving its jacked up I believe you can simulate load to a degree.