Intermittent Whistling when AC or Heat is on

[530iNoir]

I get a shrill whistle , but it only seems to occur when the AC or Heat is on. I have searched the forum, and did not see this issue before. The other posts mentioned noise when in park, but My issue occurs when driving. Any Ideas?

[jnmip]

I get a shrill whistle , but it only seems to occur when the AC or Heat is on. I have searched the forum, and did not see this issue before. The other posts mentioned noise when in park, but My issue occurs when driving. Any Ideas?

I was getting screeching/squealing noises in a similar situation and it turned out to be the blower motor (bearings failing). I replaced the motor and no more noise.

Does the sound go away a few seconds after turning the fan off?

[gmannino]

Yup, blower motor squeals

[Airborne001]

I don't think it is the blower as I have this same issue. It is NOT coming from the compressor, but seems to only be pesent when the compressor engages.
It is only audible from inside the cabin.