have a 03 mercury mountaineer awd v6.I bought it in 2004 with 23,000 miles on it in illinois(the car was a rental in hawaii).Currently i have a little over 46,000 miles.Here is my problem:the engine runs smooth with AC off,but soon as i turn it on, the compressor makes a chaterring or growling noise.This happens at idle and when i start driving it ,under 2000 rpm til goes in 2nd the engine is very noise (engine draft?),after that is ok.I need tosay that through my vents is comming cold air,when AC on:I poped the hood and i see that the compressor cluch is engaging,the serpentine belt is very good,the compressor is tight.I have neverchecked my AC,since i bought the car,and the ac takes extensive usage during the summer.Any suggestions and informations would be highly appreciated!

maybe needs oil