DEF pump sound getting louder

[rrod]

  DEF dosing unit pump.pdf (Size: 309.75 KB / Downloads: 235)

CM2350
350k miles
DEF filter recently changed but did not fix the problem

Quote from quickserve:
“When a driver turns the key OFF, the dosing system will run a purge cycle during shutdown to prevent DEF from being left in the system and freezing in cold climates. An audible click and pumping sound will be heard from the DEF dosing unit when it is in the purge cycle. The DEF dosing unit will move its reverting valve, changing the direction of flow for the DEF. The DEF dosing unit will pull all of the DEF out of the DEF dosing control valve and line. This unused DEF is returned to the DEF tank. After a complete purge, the system will be free of any remaining DEF.”

So that sounds is getting louder. Any ideas ? I just need that pump to survive for 5 more months :s