I have an Intertherm electric furnace in 7 yr old manufactured home on the Oregon coast. Recently I noticed that the fan doesn't always blow at the same 'strength'. Sometimes it runs the same speed for the 30 or 40 seconds that it is on, other times it seems to run faster at the end or have a slow spot in the middle. I change the filter twice a year, we don't run it from may to september, and the wiring looks fine. Is it about to fail or is this normal and I have never noticed before?