e46 1999 316i m43b19 squeeling sound after engine hot

Hi
For some time now I`ve had issues with a terrible high pitched loud squealing sound. The sound seems to be from the engine bay or under the front/middle part of the car.

• The sound appears after driving the car about an hour or so
• The sound is constant with little variation
• The sound seems to be loud all over the engine bay
• The sound is the same at all rpm, maybe a little less loud when accelerating but might be just hard to hear.

I`ve replaced both "fan" belts, and the (3) pulleys except tensioner pulleys

What I`ve tried to diagnostic the issue (with squealing sound present) :

• Spraying silicone grease/lube under the old fan belts to see if the sound went away, without any change in sound.
• Listen with a metal rod to identify the squeal (I did not locate the sound)
• Changed my belts and pulley's without fixing the sound.
• Blocking the exhaust with a rag. (no change in sound

Please I need some tips, I cannot seem to find the problem and it`s quite annoying.