Is this the amp you had fixed? If so they might have neglected to put back some shield or internal ground or something. Exactly what kind of noise are you getting, and is it there even with zero volume on the HU? How about with the RCA's unplugged? Does it change with the amp gain?
1999 Buick Park Ave Ultra
Head Unit: JVC KWHDR720
EQ: Audiocontrol EQL
Front Stage: Hybrid Audio Technologies Imagine 5.25 mids, Morel Maximo tweets
Sub Stage: Boston G3 10", 0.5 cu ft sealed
Amp: PPI Phantom 900.4
Rear Fill: Boston SE953 6X9's