Pinging or Valve clatter sound between 1700 & 2200rpm's, I have tried all the injector cleaners, went out and towed the 5th wheeler around for a few hundered miles keeping the temps around 800 to 1000 deg and its still there. When the box is turned off it's still there but not as loud,so my question is this just the noise the injectors are going to make the older they get or do they need to be replaced? 35000 miles to date and #3 injector has been replaced due to failure.