So this vibration has been going on for quite some time now. Now it only happens when the air is on and im at an idle. If im idling somewhere like at a light for example while the air is on, the car starts to vibrate not serious vibration but like a pulse vibration like bahhh....bahhh...bahhhh..so on and so forth...BUT if i put it in park or netural it stops but when i put it in drive it vibrates....now it only happens when i idle nothing going on as im driving around......I just want to make sure this is normal or if something wrong.....