The speakers are located near the knee area not easily accessible and would require removing the complete dashboard.
I am not sure warranty will cover this situation as there is no problem with the product. It is self inflicted.
I tried compressed air from my air compressor but it did not help.
The best result I got when I spanked the area where the speaker grill is located with with hand, it did help a bit and a lot of sand fell off behind the dash. The crackling sound came down but still present. I ran the speaker with full volume to agitate the sand off, it hardly helped.
While installing A Pilar spotlights this week I asked the garage people to clean it a bit, as they were putting a switch in the vicinity the cleaned a bit more. But a faint distortion is still present.
I too had issues with sand getting stuck in the AC buttons. When the service manager saw my car without a roof he had advised me to ensure they are kept clean, since otherwise the buttons could get jammed. Luckily it was not severe in my case.
I don’t think Jeep service center does any work to clean the dash of sand, and even if the will do, it will cost a ton.