I wasn't clear - sorry. I'm not advocating changing the sand but inspecting the laterals (which are buried at the bottom of the sand) before buying a new filter. It sounds like either your laterals may have been broken since the filter was installed or (as you surmize) the pump is pushing sand through them. The only way to know is to inspect. I see the laterals for Hayward S310T2 (2004 and prior) for as little as $5.00 on Amazon (not including shipping) where the S310T2 filter with multiport valve is more like $500.00. I would find a way to save the sand as I removed it and reuse it.

Here's the parts list for the S310T2 if that's the filter you have and here's the manual.