Thread: car only getting 15mpg. and a screeching noise from rear main/flywheel area

Does the squeal go away with the oil cap off?

You are either putting to much vacuum to crankcase through the PCV valve on the supercharger. (No o-ring or bad valve)

or

The PCV passage is blocked that goes from front of supercharger to the throttle body. This passage lets metered air into the crankcase.

Again, take cap off and the squeal should go away.