Alternator whine from TCU BT module

[TechieCarGuy]

I've spent a lot of time trying to trouble shot some engine noise as part of a stereo upgrade, which I started shortly after buying my 2010 135i with Nav'.

The noise is alternator whine which increases in pitch when engine is running and as rpm increases. The interesting thing is even with all my aftermarket equipment disconnected including all speakers, the noise still persist.

Today I made sure all my aftermarket equipment was disconnected and did some searching with my wife in the driver seat and tapping the accelerator. Even with no audio equipment in car their is a slight whine coming from the TCU unit in the trunk.

Has anyone experienced this and is it possibly an indication of a bad TCU or maybe my alternator is at fault and going bad? I have a new battery, less than 6 months old and as stated before have removed all other possibilities.

With no speakers in the car I am not sure how this noise is being generated but it is there?