Nice job on getting some coverage for yourself...
Was it the video how they did it or was it just ur car, It looked like some of those drifts were at like 25-30 MPH. And sounded like the car wasn't in the right gear a few times...
Anyways NICE JOB!!!!
I would say get a ground loop isiolator on it, and then get an engine grounding kit... Also I noticed on my car i had the same problem, switched head units and BAM it was gone.. Just try it.. But yea grounding it thru the chassis and not the factory harness should help too...