I have a whining or buzzing noise through my speakers when volume is at 0, may be there with the volume up I don't know.
Only happens with the engine running. Is this alternator whine?
Usually it is, I've done both and have seen that sometimes when I get a whine through the speakers it is because of that ground not being right. Bolt it to someplace behind the dash and the whine goes away. Yet other installs I have had no whine so it all depends on the car and the quality of the grounds in it from factory.
Most car companies ground multiple things to the same ground so when you use the factory one there could be more than just your radio grounding to the same point.
Grounding to the car chassis instead of through the factory harness didn't make a difference so I ran a bare wire from the screw near the rcas and touched each rca shielding with the wire and the noise went away.