I have a Hayward S180T filter. I just replaced the sand this year and I noticed that sand will come out of my return line into the pool but only happens for 10 seconds or so then there is now more sand. This happens when ever the filter is turned on. what could cause this to happen?.... it happens after I backwash as well even after I rinse for 1 minute. Would a cracked lateral cause this or would that be constantly sending sand into the return?