Where is your tensioner mark lined up? Can you take a pic of it and post it? Couplers don't squeal AT ALL. It'* not possible.
Remove your SC belt and start the car (this belt also drives your water pump, so don't run for more than a minute). If the sound is gone, spin the SC by hand. Hear anything? Feel anything? Wiggle the pulley around. What do you feel or hear?
Now put the belt back and start the car. Squeal back? If so, where is your tension alignment mark on the SC tensioner?
You'll have to remove your SC from the car to do ANY work. If you have to replace your nosedrive, you're best replacing the needle bearings on the other end at the same time, and the coupler due to age alone.
How'* the oil level in the SC?