background noise linked to rpms

just like to say that this post made me feel very confident that i wasnt wasting my time trying to find a better ground spot.  thank you.  the whine goes away when i disconnect the rca from the amp itself.  my ground was the connection between the back of the seat hinge and the floor (the seats fold down so there is a large metal plate, for stabilities sake i would assume).  i think the problem lies in the paint that is lightly sprayed over the body of the car that is keeping the seat metal from being in direct contact with the body.  i think i found a spot BUT, it is not a direct contact, it is a piece welded to the car body.  My next question is wether the weld would alow proper electrical travel? i used the stock radio grounding, and i have not changed anything as far as the big three...

for those who asked, i am using a sony head unit, i forget the model but it is the cheapest ($75) one with the aux connection.

and by the ohms matching, i followed the tutorial for checking the rca ground and it said to touch the headunit case and the rca sheeth and see if the ohm output matched and it did, at about .5 ohms i believe...

also, i was showing my dad the sound it made to see if he had anything to add to my research (he has a somewhat random wealth of knowlege, so it never hurts to ask) and it didnt happen.  i tried a few times and the sound wasnt there.....but this morning when i went to work it was. idk

Check the return resistance at your proposed ground spot.

Have you tried turning the gains of the amp all the way down?