I think I'm hearing a sound related to the transmission (1991 Honda Accord automatic transmission) because I saw the "S" indicator go on and off (more than once) but it doesn't happen very often (perhaps days or weeks between episodes) and I don't notice any slippage in the automatic transmission's shifting. I checked the fluid and it looks like new and full and see no leakage underneath. The best way I can describe the sound is that it sounds like the car is in a higher gear because of the louder sound but it's in the proper gear. I had a local shop look at the car and they couldn't find anything (including a road test) and said they barely could hear the noise I'm hearing. I've had the car since new so I know it's behavior/sounds well and know I'm not imagining it. Just wish it was more obvious to others so it would be easier to diagnose. Other than sound, the car drives fine.
Could this have anything to do with a bad " Transmission Control Unit " . What symptoms will a faulty " Transmission Control Unit " in a 1991 Honda Accord give? Will it cause any unusual type sounds as well?