2000 Impala RDS radio amp install problem

[stokasz]

I am trying to install a small 4 channel amp into a 2000 Impala with the RDS radio. I bypassed the stock amp because I had the "104" unit that had no bass but wanted a little more power to drive some aftermarket speakers I installed. The problem is I can't get the stock head unit to output at line level by grounding the amp sensor wire. The output is lowered but if I attach the rca shield wire I lose all sound. If I unground the amp sensor wire and I try to use the hi level input on the amp everything works fine until I start the car and I get loud alternator noise. I tried line filters, different grounds, isolating the amp but nothing eliminated the noise. The alternator noise seems to be actually on speaker output from the head unit but there is no noise when I connect to the speakers with the amp bypassed. Does anybody have any experience with this problem? Thanks for the help.

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