2006 Hyundai Elantra • 4 cylinder FWD Automatic • 30,000 miles

I drive a 2006 hyundai elantra with around 30,000 miles on it and lately there has been a rattling noise coming from the engine bay. It happens around 2000 rpm and only in drive. I narrowed the noise down to the area around the waterpump and alternator. I also tried turning the AC on and off and I found that the noise was greater when the AC was turned on then when it was turned off. What could this be and how can I fix it?
December 8, 2010.

Check A/C idler bearing for noise, take off belt and feel for rough operation or noise when you free spin it.

Mark (mhpautos)

Dec 9, 2010.
Checked that and it ran smooth without noise. I also went around and tightened every bolt I could reach. There is another problem, I dont know if its related but, now im getting a check engine code 2270 saying that sensor two is lean. This code pops up and goes away at seemingly random intervals. The noise also has developed into a sporadic sound. Sometimes it is there and other times its not. I took the car to a mechanic and replaced my A/C compressor but the noise and light still remain. What else could it be?

Jan 18, 2011.