hi, i have this common problem too. i 've had my dishwasher for 12 years and yes i do everything that you do, wash the filters, salt it etc, what i found in the end is to remove the filters and every other removable parts, put the special cleaner bottle in the cutlery holder upside down and put the washer on the longest wash without any filters in. afterwards use paper towels to soak up the water collected in the hole and any residues and start with a nice dry dishwasher, refitting your filters and most important of all MAKE SURE YOU HAVE FILLED THE RINSE AID UP , using a good quality one and check it's volume regularly. Make sure also that you rinse excess food off your crockery etc. i find that the above keeps everything going smoothly for a fair while and you will know when to do it again when the sandy stuff is back again. It also may be you are more prone to this if you are in a hard water area like me, i don't know if this is relevant but i was thinking along the lines of limescale which i think it is which is why we add the special salt, anyway, happy new year and hope this helps, best of luck.