High mileage E9x M3s will spring an oil filter housing leak. Rubber gasket becomes brittle, just like the valve cover gaskets, which are prone to leaks. Oil hits the belts and they make noise.
The idler pulleys have bearing that wears out and causes the whistling to, like a supercharger. The hydraulic tensioners also fail. So change it all when you change the belts.
Good to know that the plenum can cause the whistling sound. Fun way to fix that is to get a custom painted M3 S65 plenum from IND, and return your core. Great Price!!! Can't wait for my TVAs to fail, so I can do this...HaHa.
https://ind-distribution.com/collections/m3-e90/products/ind-painted-e9x-m3-engine-cover
If you have a E9x or F8x M3 in LA, there are great Indie Shops to visit vs. BH BMW.
The Federal EPA 8 yr/80k mile Warranty covers your TVAs and ICV, but no BMW Dealership SA will tell you that....especially if your BMW warranty has expired.
UPDATE: Whistling was still there after the oil filter housing and pulleys/tensioner/belts were replaced in Feb. 2020.
ICV and Fuel Tank Breaker Valve were replaced in Dec. 2019. Defective ICV/FTBV causes jumpy idle and not the whistling sound. I also have the Eventuri Carbon Fiber Intake and Airbox Cover that I installed in mid-2019, which resonates nicely, but doesn't cause the whistling sound. Unless you have a supercharger, the plenum ICV hose inlet is the likely source of the whistling that changes with accelerator position. Also check that each of the 8 throttle body rubber gaskets/hoses is properly seated under the plenum. If not seated properly or brittle, the plenum will crush the rubber piece and cause a leak (BMW Dealer did this once).
UPFATE2: The whistling sound can be recreated by driving on the street at 30-55 mph in top gears 4-5-6-7, then take your foot off the accelerator and then back on while reving the engine from 1000-2000 rpm. Then you can hear the whistling. You won't hear the whistling at highway speeds at 2500-3000 rpm.
A new S65 plenum is $1100-1300, plus $120 for the //M V8 emblems. Try to find a low mileage used one on ebay or deans bimmer or your local BMW Indie Shop, if you don't want to try the RTV leak fix.
Darn...a Custom Painted IND S65 Plenum was sooooo close.
https://www.m3post.com/forums/showthread.php?t=528247
dreamspeed just saved me a ton of $$$$. Thank you!!!
Cheers