I have a S240 sand filter with a side mounted multivalve on an in ground pool. I dont know if it is normal or not, but it seemsand sounds like there is air going thru the multivalve only. The skimmer of front side of pump is clear with no bubbles. I get the same sound whether it is on recirculate or filter. I see no water leaks and no bubbles coming out of jets or in SWG? Please chime in with help/advise and thanks in advance!!!!