Law enforcement sources tell TMZ Selena's Hidden Hills, CA neighbors were so pissed off at the loud noise coming from her house at around 11:30 PM ... they called police. The cops responded and warned Selena and company to turn down the volume or else. One neighbor tells TMZ the noise was so ear-crushing her windows were rattling.

Sources connected with Selena and her family tell us he singer has told her kinfolk she's back with Justin Bieber because he's cleaned up his act. But they tell us they don't think it's coincidental at all that in the last few days she's spent a late, late night at a Hollywood club with Bieber and had an out-of-control party on a Tuesday night.