Originally Posted by ontopofm
there is still hiss after the speaker inputs wire is disconnected from the alpine amp, so the amp is bad? my question is, if the input is disconnected, then there is no signal going to the alpine amp, then why is it bad?
Then it is the noise of its own. Normally such aftermarket amps have S/N rate higher than 90dB, even my PDX with 76dB doesn't have any noise if input is disconnected. Above 90dB should be noisefree absolutely. I assume your car engine was off during the test otherwise the electric magnetic interruption could also be a possible noise origin.
So you could send back you amp.