We have an 13/14 year old ICP/Keeprite furnace (NUG5100BFB1) and a few months back, others in the house complained about noise from the furnace during quiet periods. The furnace is heating the house OK but it seems to go into a mode where the exhaust blower comes on for 20 seconds, then goes off, then comes on 20 seconds later, then goes off, etc. Because it does fire up, and heats the place, I figured this was not a critical problem but now it's just driving everybody crazy! I'm not even sure if it was always like this or if its new. I have checked the filter, vacuumed dust etc., checked wiring connections and everything seems to be normal. There is a Honeywell CT3400 thermostat controlling the system. Gas usage seems to be consistent and there are no gas smells around furnace. Any ideas before calling in a tech?