I don't know if the hatch is causing your beeping issue but you can check if your is closed by using your interior lights. Set your light switch is set so that your interior lights come on when the door is opened, and then fade out after about 10 seconds when the door is closed. If your hatch is not securely closed then the lights will not fade out but stay on.

As for the bumper adjustment I thought I read somewhere in the maintenance manual a complete procedure for adjusting the bumpers and torquing them down 88 in-lbs but can't find that info now, at least in the standard Crossfire manual. Will see if I can get a copy of a manual for an SRT6 and look in that.