Replaced the power liftgate motor, mystery beep still there! The beep started once the temps got back into the 70's. I'm done fucking with it if something finally stops working entirely then Ill know whats broken. My only thought is to pull the fuse for the rear folding seats but Im done for the meantime.
I drove my '99 Gas V10 F250 (Lifted 4wd 31" tires) 850 miles to Barber one summer. I think I stopped for gas 8x. When I got home, I put new mufflers in.
Thats probably the fix. The speaker is in the liftgate. It makes the chimes for the power liftgate and the back row power seats going up n down.