Is it ok for compressor to be disconnected? What do I need to be aware of?

What is your question?

Had trans rebuilt a year ago, now having trouble pressing in button on shift to shift out of park when cold. Some noise from front end started around same time. When checking, I also starting hearing some noise from behind rear passenger tire when key turned back. (2000 GMC Jimmy Diamond Edition 4x4 has a compressor in rear to use for airing up tires, etc...Mine is missing coverpanel so I later figured out had been accidentally turned on from something rolling into it...noise went away when I turned off). Anyway, I took it back to trans shop to check but shift problem didn't happen since it was warmer that day but I was told that the compressor was causing the front end noise and they just "disconnected it" since it wasn't "hooked up" anyway?? I've tried to research if this is ok & what all is run from it but not finding much. How could this have not been "hooked up anyway" if it was making noise? Likey they disconnected a year ago when rebuilding my trans? Wish I could find diagrams for things on this truck. PS - took to another shop - noise was alternator Thanks!