I am not sure what the problem is, but every once in a while it is like some system turns on and it sounds like a fan of some sort is rumbling, then the system cuts off and it goes away and the car sounds perfect. Any ideals?

Also yesterday for a minute or so the smell of burning plastic came through the vents, wierd

 

Its probably your SAP (secondary air pump) going out. They usually turn on when the engine is first started. (kinda sounds like a vaccum cleaner when they go bad)

 

very common on most cars of today ( secondary air injection ) mine buzzes a bit but normal on cold starts

 

If the vehicle has been run for awhile it might be the auxilary cooling fan for the radiator. The usually happens after driving for awhile andthen idling in traffic etc. or going slowly without a lot of air passing through the radiator