Sand coming from one of the jets

Hello all,

I have an in ground vinyl lined pool with a DE filter. The filter runs fine (about 17 PSI which has been about my norm), the water is clear, and I can vacuum it just fine.

However, one thing I noticed last season is that from one of my jets (the farthest one from the filter) blows sand into the pool during the first, say 5 seconds when the filter is being turned on.

I don't think there's a leak otherwise my pressure would be low. Any ideas what this might be?