Recently my car started making a high-pitched whistling/whining noise that belt dressing did not fix. My question is this...when facing the engine, what is the bottom left pulley attached to (what does it do - the one attached to the bottom of the engine block)? All of the other pulleys that have bolts on them are still, but the bottom left pulley is vibrating/turning so that the bolt is definitely not still. Is the bolt supposed to turn with the pulley? If not, do I just need to turn the bolt (if so, to what torque)? Any other suggestions as to what could be causing this noise?

Thank you in advance for any help.

 

It's supposed to turn with the pulley. That is not your problem.