A squeaky belt is usually caused by a bad belt, a missaligned pulley, or something leaking on the belt.
Either the belt is worn out or the tensioner is defective.
the seat
Your local auto parts store should have several different brands in stock of belt dressing for squeaky drive belts.
oil it or shoot a squealer
Yes, as long as there is no damage to it
Sounds like a belt or belt tensioner needs to be replaced
Replace with Good Year Gatorback belt. Costs more but worth the money.
Make sure you are not latching it into the buckle for the middle seat belt.
a seat belt law is a law of the road
Seat belt cilker.
wear a seat belt.