Buzz / whine from speakers - aftermarket HU
I've got a 52 plate audi s3 which when bought had an aftermarket HU fitted (Kenwood KDC-237), non-bose with sub (no amp) in boot. This clearly wasn't fitted properly as I have a dim buzzing/whining noise coming from the rear speakers which gets louder/softer with the revs of the car.
I understand that this is due to excess power being sent to the rear speakers and causing interferrance but I'm not sure how to fix it. From reading other posts, people suggest using the PC9-404 leads but that seems to have a double black plug inserting to the HU but the Kenwood has a single plug. Therefore pretty sure that this won't work, any other ideas?
I know there are a few other threads on this but none of them seem to raise the same problem.
Any help would be greatly received (I'm not an expert electrician so any help will need lots of explanation...!).
Cheers in advance - this noise is driving me !