99' Taurus airconditioner problem?

Okay, this is a weird one...the air works fine..havent been using a heck of a lot of it..but when I went to back out of the driveway..started hearing this noise..only way I can describe it..is it sounds like a fan hitting something (but its not).....when the air is off..the sound is really loud..but when you turn the air on..it gets a lot quieter..after the car is shut off..you can hear what sounds like air leaking from something, only lasts a few seconds :headshake (that might be normal after the air shuts off..i dont know...never put my head under the hood after I turn off my car when nothing is wrong)

Cant get the car in to get looked at till Thursday..so I was hoping for some advice on what it may be....water pump? Clutch in Airconditioner?

Rust In The A/c Clutch - Not Uncommon If It Isn't Used Much

Rust In The A/c Clutch - Not Uncommon If It Isn't Used Much

Yep pretty much what it was the clutch..and assembly loose...to the tune of $850.00 *sigh* Here you think your doing a good thing from not running the air all the time.