My gf's car get a strange rattling sound when you turn the A/C on only when the car comes to a stop in D (Drive) does not do this when you are stopped in Park or Neutral. Any ideas as to what it could be?

Also any time you fire up the car it makes a quick whistling sound, any ideas on that?

 

Most rattles appear when the car is on "D" or when A/C is on because there is a load on the engine and it causes the motor to vibrate more. I would recommend to pinpoint this rattle and fix it or buy some new motor mounts.

Can't help you with the whistling noise..

 

whistling is usually the air ;]

 

Ok so I changed the bearing in the idler pulley and squeaking/chirping sound is still there
-Could this be the fan clutch by chance?
The whistling sound right up startup is more of a quick squeak.