This is one reason I believe extended warranties (except the 2nd year extension offered by FR but NOT advertised by &^%$^%& dealers) are not worth the paper they are printed on.
You can buy a NEW Shurflo higher pressure QUIET pump for about what you have paid for troubleshooting so far. Unscrew the old one; screw in the new one and done. If it did not solve your issue, you at LEAST have an upgraded pump AND you eliminated the 90% probable cause. Hypro-shurflo Llc - SHURflo Whisper King Demand Fresh Water Pump - Pumps & Tanks - Camping World
The remaining causes involve plumbing only and involve a little "head scratching on your part to find and repair. Why pay 150 dollars an hour for a technician to "head scratch"?
Once they tested the pump (and it passed), they were "done" and your problems just started. Because FR would only pay for the repair IF A PROBLEM was found, the repair shop did you no favor with a CND finding (Could Not Duplicate).
Just like a car "rattle," finding it yourself is the only cost effective way to get it fixed. A mechanic can shoot hours "not finding it." Buy a stethoscope and have your DW take it for a drive while you "listen for the noise." The quarter that slid down the defroster vent will show up eventually.
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW