Pools, Spas and Hot Tubs - Sand in the pool

Hey guys,

I just got this house and don't know much about its pool's history.
Anyway, for some reason on startup of the pump I have a little bit of sand thrown in in the pool out of return. It happens only on a pump start up, I tried to cover return with a fine skimmer sock after about 5-10 min after startup and see if I get any sand and there was none.

Sand also comes out on backwash. I did rinse after the backwash but still getting sand every time pump kicks in.

Do you guys think filter's Lateral Assembly is shot or there is an issue with the valve?

It's Hayward Pro series filter.

Also if it is lateral and I will have to disassemble the filter, any recommendations on Sand Alternative media? or should I just stick with regular filter sand?

Thanks

How fine is the sand ?

If the grains are large, then I suspect a lateral.

If very fine, then you need to vacuum to waste after letting it settle - or you will just repeat the cycle.