Originally Posted by BT17R

With A/C button off, compressor will only come on if controls are set to Defrost or Max Cold.

Hmm, the noise. How long was the engine running before it's heard? Is the engine fully warmed? Is your foot off the brake? Can you pinpoint the location by listening under the hood? Is it continuous or intermittent?

The only other things that come to mind are the emissions control system is scavengering tank vapors through the charcoal canister, or the gas cap wasn't fastened correctly. Try R&Ring the cap again, the new caps no longer ratchet continuously so maybe it isn't fully seated.

That pretty much plays out my ideas other than a loose/leaking vacuum line, but I'm sure that would throw a MIL. Time for the dealer to check it out at the alignment. Good luck...