I have the same problem with my 99 SL2. No clue what is wrong.
The belt is loose and needs adjusting, or it is worn out and needs replacing.
That is normal when revving.
saturn is outside the asteroid belt
I believe you need to replace a timing belt. Cause it uses timing chain which doesn't required to change as timing belt.
I would check for a loose alternator belt.
Saturn lies outside the asteroid belt.
Check the alignment of belt in relationship to all pulleys. Check the condition of the pulleys. Also make sure the belt being replace is the recommended size. Auto shops have belt measuring tools to check the size of the belt before installing into your vehicle. You may have had a belt installed that was too large in the first place. The squeaks are a sign of a loose belt or a belt not recommended for your vehicle.
This may, or may not be applicable, depending on if you had tried replacing the serpentine belt also. One cause for this would be the belt-tensioner has weakened and is not applying sufficient tension on the serpentine belt, allowing it lose traction on the pullies.
Replace or tighten the A/C belt. If equipped with a serpentine belt, replace it.
belt
Weak alternator? Bad Voltage regulator? Alternator belt slipping?
At or before 100,000 miles if snaps it will cause much damage.