can’t get rid of alternator whine

i put some gear in a friends car a few months ago, pair of pinoeer 6x9s running off a jenson 4 channel amp. all was fine and it sounded good, just recently he got his friend to install his subs and amp, in the process, he's shorted out the rca's and blown them so now theres tonnes of whine through the 6x9's. tryed regrounding the amp, its currently grounded to a seatbelt bolt, tryed an RCA noise supressor which didnt help at all, then tryed a Power cable noise filter, made a difference but still overpowering whine, are there any other options without replacing the head unit?

thanks in advance :)