oscillating buzzing over bluetooth Pioneer 80PRS

[Bun-Bun 10+ year member]

People talking to me on the phone complain of a buzzing sound. I have borrowed my gf's phone and confirmed this myself. It's fine on my end but for the person on the other end there is a oscillating buzzing sound.

I have tried connecting my gf's phone to the headunit and calling my phone. Noise is still there (Hers is an iPhone 4S mine is an HTC One)

I have tried disconnecting the mic to see if it was picking up something. Noise is still there.

I have tried disconnecting the radio antennae and cutting the illumination wire. noise is still there.

I have tried disconnecting my amps and turning them off. Noise is still there.

The HU is wired directly to the battery in my trunk (separate from the car battery under the hood).

Noise is present whether the engine is running or not or whether the key is on ignition or accessory.

Next I am going to try taking the HU out of my car and running it on my bench with a power supply.

Any other ideas? I am really starting to think I have a dud HU.

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[Bun-Bun 10+ year member]

Still does it. Has to be the head unit.

Local dealer doesn't want to replace it.