Mine did the same thing. I took it apart and it wasn't out of balance, but one of the bearings inside the motor was really loose. I replaced the motor with a buddy's who had one go bad, I used the good one of the two. It lasted about two weeks and did the same thing. I've put my stock fan back on for now, which doesn't do well at all with my front mount. I may buy another ramcharger style dual fan. Mine lasted a couple of years and for $80 bucks, I'll replace it every two years if I have to. I'm sure there are fans out there that can stand the underhood temps we have, but you'll probably pay quite a bit more. Just my opinion.