Came out to investigate thumping and grinding noises. I was unable to locate any thumping sounds. From customer’s description, it sounds like duct work expansion, which is normal, but can be controlled. We’d have to come back if it continues. The grinding noise was identified as the blower motor. The bearings make a very loud grind when it initially starts and it continues through the heat cycle. Average life of system is 12-15 years. Unit is currently 16 years of age. Due to age, condition, and repair costs, I recommended a second opinion. Failure is expected. Dan Fox will be in touch this afternoon to discuss options.