I have ben putting alot of work into my blazer. Just got done doing the ball joints, idler arm, and pitmen arm. Now for some odd reason I have a very loud annoying buzz or humm any time I turn on the heat or air. No matter how high or low its set it makes the same constant volume noise. I am sure someone has ben through this before so if anyone knows a way to trouble shoot this or knows exactly what it is I would be very happy to hear. Thanks in advanced.

 

My 03 blazer makes the same noise when the compressor kicks on when the compressor kicks off the noise goes away. but mine has been doing this for about 40,000 miles haven't had any problems with my ac. However, I think its low on oil but, I never had it checked. oh, at an idol its loud but driving down the road its quite.