99 camaro Z28 5.7 liter V8/Auto/12,000 original miles.Theres a metallic grinding noise coming from the left side of the engine. The metallic grinding sound stops when I either put on the A/C or defogger. So to recap I hear metallic grinding noise...and when I put the A/C or defogger on I then hear the clutch engage and the metallic grinding sound goes away. It immediately comes back on when I shut the A/c or defogger off. I noticed the belt tensioner on the top left of the engine shakes. I put more tension then less tension and the noise is still there. I dont believe its the belt but its possible.Maybe a pulley is loose or needs replacement. Maybe its the tensioner pulley. I dont have any idea. Any advice? Thank you so much in advance. Please reply to cobrakillr718@yahoo.com

 

Might be the clutch on the A/C compressor going out.... Or the bearing on the tensioner, possibility....