I have a 2004.5 Dodge 2500 With the 600 Cummins, when I turn the key, sometimes there is a loud humming noise that last about 5 or 6 seconds and then when I start it, a clicking noise, that clicks about ever 10 seconds when idling, if the headlight are on it will dim them ever time it clicks, till the truck is warmed up. I think the loud humming noise is the fuel pump, but not sure. Are these noises normal for the 600. Thank you

 

I assume the humming is the cp3, doesn't sound like it pushes thousands of pounds of pressure does it? and the click and dimming is the grid heaters cycling. Yes this is normal

 

The noises you hear are completley normal, the clicking is rapid cycling of your heater grid for your air intake. As you may know diesel engines work by fuel being injected into extremely hot compressed air, causing combustion. The grid is similar to a hair dryer in function. These are the reasons why you see your lights dim after it is started. These trucks are set to cycle the grid for 4min? after start unless you go over 18mph? Then it shuts off right away. So just think how much juice it takes to cycle these heaters. Most hair dyers for example are over 1000 watts, thats a lot of juice to pull from a car battery. that is one reason why the cummins comes with 2 batteries.
hope it helps.