I just had this happen the other day too!!!
Yesterday I spliced the pink wire from the onstar/bose wiring harness to the new remote turn on wire (blue/white) worked like a charm!

Then I mounted all my panels back on the car start the car and the damn back speaker is buzzing. And as I accelerate the buzzing becomes worse.
I have a feeling it is either to do with my alternator interfering or else there is a ground wire somewhere that I did not connect?

I am running a Scosche fai3a converter from the bigger harness through to my new Head-Unit. I believe it is set to common ground option at the moment.

Anyone else have any experience with this or a similar set-up? I WANT THIS BUZZING GONE!!!

Thanks in advance for any help with this!