I have a Trane XE 70 furnace, manufactured around 1990. It has been serviced yearly since I purchased the home 6 years ago. About 2 months ago it began making a low pitch rumble after the burners ignite and before the fan kicks on. The rumble occurs 35 seconds after the burners ignite and lasts 10-15 seconds. I recently had a service tech. come to evaluate the situation and he didn't have a good answer. There are no visible cracks in the heat exchanger and no carbon monoxide leaks into the home. The only suggestion he had was to replace the furnace. I'm hoping for a more reasonable explanation for the rumble.

If you had a qualified service person at your residence and they could not find a problem do you believe that someone long distance can? Sorry but these kind of problem have to be seen and heard at the site. If anyone says different then they must have a crystal ball.