Well, I have no manuals from the previous owner. The sound is coming from the return pipe from the sand filter. I was going to replace the o-ring on the sand filter. It has a small leak when it is running...plus my multivalve is sometimes wet when it should be dry (esp during the day). I am hoping that might solve the noise issue. Do you think I might need a new multivalve?????

I am just curious about the sound...if is being caused by air or I need to replace something.

thanks, I'll try the DE in my filter.