Is my pump/filter operating properly?

I have a 2-yr old 24" AG with a 1 HP Hayward Power-Flo LX pump and Hayward S166T sand filter. The Filter outlets to a Hayward chlorine feeder that has nothing in it. The pump primes fine and filter is operating normally. When I turn on the pump for the first time (after it has been off a while) if runs noise free and there's a strong return of water into the pool. However, when I go to check on it after a few hours, the pump seems to be making a *little* bit more noise than it did when I turned it on, and the return flow into the pool is about half-strength. If I turn the pump off, then back on, it returns to normal: quieter operation and full-strength return. Any ideas? thx.

During the transition from good flow to low flow, what does your filter guage do? Have you backwashed?

The filter is solid on 21 lbs. I backwashed last week, no change. Thx.

Wow! That's a puzzle!

I can think of nothing that would cause a drop in flow without a resultant increase or decrease in filter pressure. Sorry I can't help.