HVAC whirring noise when engine on

[Scott.b]

Hi folks,
Recently picked up an F80 M3 and there is one sound that is really bugging me. When the heating fans are on in the car i seem to get a noise transmitted to the cabin from the engine bay - its like a whirring noise.
It happens both when the AC is on and off but doesn't happen when the fans are on and the engine is off. The noise seems to follow the revs as well.
I've searched the web high and low and seems like this may have been an issue with N55 engines and it needed a weight on one of the AC hoses (SIB 64 01 14). Having checked the AC hoses today it has this weight so suspect it is something else.
Has anyone had anything like this?
As you'd expect its near impossible to get the sound across on the video so not attached it.
Any help appreciated.

[rockstar b]

Maybe something in the blower motor?

[Scott.b]

Forgot to mention that the blower motor had been checked and it's not that.

[L0vem3]

Any update to this? I've noticed this as well