beeping under left side of dash

I have a 2002 malibu. When idling in park i hear first one beep,
then after 6-7 seconds 2 beeps, 6-7 seconds 3 beeps, 6-7 seconds 4 beeps
no indicator lights are on, sound like it's coming for left side near where the
emergency break is
Is this hazardous?

Rear Seat was folded down..probably caused the beeping..seatbelt related?
Who knows.dealer said there was nothing in my car that could make that sound. Thanks Chevy!