A/C Compressor noise?

[crazyd]

I've had this happen now with three different compressors in two different GPs. Between 2000 and 4000 rpm, I get this groaning sound from the compressor. I've done the exact same recharging sequence each time - vacuum system down, add 8oz. ester oil, add 2 1/2 cans R134A. Cooling is working fine, no other problems besides this noise. I doubt it is normal. What is the problem with these stupid compressors?

[tunerlover3]

Is the noise only there with the AC on?

 

[crazyd]

Yes.