Had the tank pumped out yesterday and noticed the shaft style aereator, original to the Jet system and 30 years old was a little noisy. Started looking for a replacement and most aftermarket clones have a 'notice' that their unit is designed to only run continuously. Mine is on a Jet timer and runs intermittently. Even though I installed this system in 1990 myself I can't remember WHY I set it to run 'on and off' but no doubt I followed factory instructions. Does anyone know???