Should an amp make a hissing sound....even after the car is off?

[Ursula1000]

I had an Alpine KTP-445U 4-channel amp installed on my 2012 Scion xB. There is a small hiss when music is playing and when I shut the car off, the hiss continues for 15-39 seconds. Is this normal? Also, the volume is ear-splitting when I raise it to 25. Before the install, when the volume was at 25, it wasn't loud. I used to have to raise it to 40 for it to be somewhat loud. Is it the gain? Any help would be appreciated, thanks.

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[whitedragon551 5,000+ posts]

Try setting the gain to low. My KTP445 never did this.