There have been noises when I turn on the A/C, mostly on R or D, but little when on N or P. It is a regular noise like the heart beating, just a little faster. Garage people said that it's the compressor needs to be replaced, since there is no leakage of the refrigerant. Weird thing is that even when I turn on the heater, the noise is still there. Is it the compressor going bad? Why the noise is still there on heating then? Thanks a lot.

 

it is prob. the bearing on your idler arm. not sure tho.