The drum exhaust fan was causing bad vibrations once the roaster warmed up. It was time to check it anyway (every 2 months) It was out of balance due to crud on the blades. Took the fan out of the housing and ground it down and polished it. After re-installing the vibration was gone with slightly increased airflow that was evident in the roast times. I will cup yesterdays post- maintenance production. I have a hunch the coffee will be slightly cleaner & brighter.