Post Alpine HD-1498bt install Hissing!

[SixBanger]

As the title says, I'm encountering hissing after I had a local stereo store install my headunit last week. First, my headunit wasn't saving the pre-sets after the install, then I had to drive back (15miles) again to have them fix that problem and now no bass. I went back a 3rd time and they couldn't fit me into their day. My vehicle sounds like shit and I have hissing coming from all speakers. My car has 2 factory subwoofers under the seat and 6 speakers including 2 tweeters. I have the "Hi-Fi" stock stereo, anyway it's a BMW 08 135i coupe. I've turned up all sub options on radio, and it still doesn't hit as hard as my previous Pioneer DEH-X9500BHS. Im also using a crux wire harness just fyi. Is there anything that I can do to fix this hissing sound myself? I cringe having to go back there again having something else go wrong.
Myles