My 2008 DGC (111,000 miles) has developed a knock but it is only when it idles and only when the AC compressor is on. It is not the AC, I've already changed that. I only use 5w20 oil in it and keep it regularly maintained. Any ideas?

 

What size motor do you have?

 

It's a 3.8. I've replaced the AC compressor and the tensioner pulley. The noise only happens when the motor is under load at idle (either when the compressor is on or when the steering wheel is turned to full clock.)