not sure if you still working on this issue... what you may consider, connect your amp to alternative power, say a stand alone battery not connected to any car, and see if you still have the whine... if you do NOT have with alternative power source, then your current whine comes from the power wires of the amp

if you continue to have whine with alternative battery, then your amp is picking up the whine from the RF... the amp itself might be faulty, or you have power cables running in parallel with audio cable for extended length...