Greetings fellow Crossfire gents! Does anyone know how to help with these issues?

1). I replaced the door speakers & tweeters, along with the wires that came with them, but the passenger door speaker still cuts in/out; it usually doesn't work when I turn the stereo on, until I turn the volume way up, then it kicks on, but can still cut out again randomly.
2). There's also a loud buzz that goes away for a bit after moving the touch-screen stereo display (it is an aftermarket BOSS stereo system that was installed by the previous owner), moving the usb wires that hang out, or banging on the dash or console. I usually just choose to crank the music so loud I can't hear it anymore lol. Being on the phone or having it plugged into the usb or connected through bluetooth makes no difference. The only thing that stops the buzz completely is turning off the stereo system.
3). Also the radio signal is pretty bad. I read that it is installed inside the lfitgate glass, but I don't want to attempt taking it apart, since I cannot find a how-to video or instructions & am unsure where fasteners are. I read that you can just clean the antenna good & that will fix the issue, no?

Thank you all, and God bless!