Hey Glenn,
I just got done with the Alpine KTP-455U install.
I had already disconnected the factory tweeters on the advice of others on the Forum and am just running the front and rear speakers, (I replaced stock speakers with new from JBL).
I do not hear a hiss from my system.
I did hook the Alpine directly to the battery and also ran a ground wire from the battery to the frame behind the power pack, then added ground wires from the factory head unit and the Alpine to the new ground. I have no idea if any of that actually helped, but it seemed like the right way to do it.
Sorry I can't be of more help. I purchased the Amp and Speakers from Crutchfield, they cost a bit more that way but the Tech support from Crutchfield is great. If you got your stuff from them I would give them a call, if not you should try contacting Alpine.
Good luck,
Doug