Burning Rubber Smell

Every now and again I smell burning rubber through my AC vents. I have not been able to pinpoint the circumstances that cause this. As far as I have noticed it is very random, I will try giving better information on this when it occurs again. I will pull over and pop the hood look for anything rubbing. Any advice would be helpful, I don't want to simply over look it.

Could be a tension or idle pulley. You can check it by taking off the belts and making sure all pulleys muve free. Could also be from the wheel wells. One of the plastic covers may have come loose

thanx for the help:) I'll update if i find out more.