2001 a/c compressor question

I've got a problem with the compressor on the 2001 C5 - When I turn the a/c on, the compressor has a whine to it - so I checked the pressure on the low side, and it was at 35psi - the line sweats, and the a/c still is cold, works fine - but when it's on, it has a bad whining noise, that gets slightly louder on accelleration, when the compressor spins more. Any Ideas? Add the synthetic oil? What should the PSI be at on the low side of this system?

-Jeff

i dont know what the psi should be, but a compressor that is making noise like that seems to have a problem to me...i would try to take notice of whether it is cooling less as time goes on