I know this post is old,but i thought id check in anyway......had the same sorta problems,shut down the motor,grabbed the main belt,was able to move the belt and sc,ac,acoupla inches either way...problem solved.....bad harmonic balancer,the inner rubber assembly became de laminated from the steel outsides causing a nasty rattle,might check it out,this happens fairly frequently im told by a mechanic buddy of mine........93 ssei...150k miles