Just purchased a 1991 RS 5.0. Did an oil change by jacking front of car to get to drainplug. When I let the car back down and started it ,there was a lot of banging noises after a few minutes. I pulled the serpentine belt off the motor, started it up and the noise went away. The AIR pump bearing sounded noisy so I replaced it. Same noise when belt is in place , but not when removed. All other accessories spun quitely when checked with belt off. Stumped??
Dave

 

So the engine didn't make any noise before you jacked it up?
What part of the car did you jack it up by?

 

No noise before, I jacked it up by the lower control arms