sorry i don't get on this thing a lot and didn't see your message til now.
So the two problems you mentioned the 1st sounds like perhaps with wiring, perhaps there's a poor connection or some interference during the install along the speaker lines, I would double check that and especially at the amp.
The tweeter rattling could be from installation and i'm not sure how you did it but w/the ones I got it fits pretty squared so I didn't run into issues there.
I hope that helps. Not sure how much further advice I could give w/o visually seeing things as you know.
I posted a response to your audio upgrade. Some other member may have some more insight but I would certainly start with checking the wiring.
Does the *hissing* also increase in loudness as you accelerate the vehicle? If it does this is also called a ground loop which will also indicate and insecure ground. Also try to check for hissing when the engine is turned off. This guide may also help: Noise Suppression Guide - Noise Suppression Guide