the only thing i can think now is try disconnecting the power cable to your subs from the battery and run the vx and see if that makes any difference.. if it does you know thats where the noise comes from.. if not maybe try a new ground for it.... and if not id guess its an internal problem in the head unit
garful.. any luck with new grounds on your head unit? ive had issues with dual head units in general... one just quit on me out of nowhere.. i got nothing but whining from the speakers, not even a hint of music... another stopped sending a signal to turn on amps out of the blue