I know what you mean. Our problem was caused by corn kernals building up under the lower sieve and finally back into the fan. last year our TR-99 fan dot torn up, but that was because we had the lower sieve to far closed. Earlier in the season we had soft cobs and the pieces were getting in the grain tank so we closed the sieve and then later in the season they got to driving too fast and the corn actually backed up into the fan.