In the endless endeavor of trying to get stuff back to shape on my truck I decided to retrofit my A/C. The "gentleman" whom I got the truck from said the A/C was working but took the belt off because it squealed alot. Well the whole retrofit/recharge went well. No leaks, blows cold. I was happy, up to the point before I started driving with it on. When getting the engine up to higher rpms in each gear it started making the most god awful noise I ever heard. Its hard to describe but sounds like something is vibrating really really bad, or a very high octave grinding noise. Turn the A/C off noise goes away. I'm guessing the compressor/clutch is taking a dump, but the odd thing is the noise sounds like it's coming from the firewall area, so that really confused me. A bad evaporator wouldn't do this would it? Any thoughts would be appreciated.