Robert, with your Cummins ISC engine your fuel injection system is called a CAPS System.
Looking in from the back of your motorhome and to the right side of engine about mid way
up on the engine you will see a square housing with looks like ( 2 ) spark plugs sticking out
of the square housing. These two thing is what sends fuel under high pressure to your injectors.
The first one in front will fuel cylinders 1, 2, 3 than the second spark plug looking thing, will
fuel cylinders 4, 5, and 6. In the base of these injector actuators the square block this is where
There is many poppets and check valves. ( the square housing is a pressure accumulator).
There is a certain noise level you will hear just the way system is made and pretty much normal.
Note: do not remove the injector actuators from that square housing in any way. The injectors
actuators and housing come as one unit and is very pricy. That is where your noise is coming from.
Dave Atherton Retired Cat Mechanic