Just got done with the rebuild on my Dad's 1969 Camro with a supercharged 396. When we started it up it ran fine. Got it back to the house after a short drive and tried to back it into the garage. As soon as he put it in reverse the was a loud squealing noise. We initially thought it was coming from the old turbo 700. Had a new one built, replaced the flex plate and torque converter. Started it up and put it in reverse and the squealing returned. It is definitely not a belt squeal as it is coming from behind the engine. The only other thing I saw is it might be the rear main seal rubbing on the crank. The engine was bought used with only 2,000 miles on the rebuild. HELP!!!