I experience a high pitched humming noise coming from my engine after driving a few minutes, but it is only when i am going less than about 2 mph. It goes away as soon as i accelerate, and comes back when im almost stopped. I can put it in park and it still makes the noise. I opened the hood and couldnt tell exactly where it was coming from. Any suggestions?

 

remove the serpentine belt to isolate, also check/rotate pulleys to feel/hear if all is ok...