I have been in my new home 6 years. I have had to replace the RP10904
Cartridge assembly in the valve 5 times. It is in the master bath. It
will last about 6-8 months and then start making a knocking noise when
ever the water is turned off anywhere else in the house. It will
continue to get worse and is very annoying. It is trash getting in the
lower assembly in the spool piece that controls the pressure balance
per Delta. I have disassembled a couple used ones and could find
nothing. Delta will not say if it is ok to remove the spool but they
recommend not to. I keep the water temp at 105 deg so scalding is not
an issue. Anyone ever remove the spool piece to correct this problem?
If so could you tell any difference in the valve operation? Thanks