I just had a new DC unit put in my 2002 Gem and the reverse beeping sound was extremely loud. To quiet it down, access your DC board and you’ll clearly see the round beeper mechanism. Simple put a piece of duct tape over the end and you’ll get a nice, muted beep when you back up. So much better.
On my 05 Gem the blue wire coming from the multi wire controller plug controls the beeper
I can say from experience what @DMax says works like a charm - I have cut that wire on all my Gems.
It does not get rid of the parking brake alarm but all the others.