truck is an 06 3500 4x4. whenever I let the truck coast or start to slow, there is a loud humming/grinding noise that sounds like it is coming from the front end. not coming from the engine or transmission because it makes the noise in gear or in neutral. help!

 

Exhaust Brake? It does sound like caliper to rotor noise when slowing without hydraulic brakes applied.
Your results may vary though.

 

Check your front axle u-joints. I've seen them get loose to the point where you can hear them rattling at low speeds. Once you speed up, the noise disappears.

 

Maybe a front wheel bearing? That is how my sounded when it was going out. Jack up your front end and give each tire a spin and see if you can kinda make out the sound. Mine was pretty hard to turn and could lightly hear the noise when I did that.

 

don't think it has an exhaust brake, I'll jack the front end up and check the brakes/bearings/ujoints

what does a new wheel bearing run? truck has 70K. other than this it's immaculate (click link in sig)

 

its been a while since I had to replace them but when I got mine from dodge I beleive they were around 130 or something like that. I have come to realize milage doesnt matter with these new sealed bearings. I had one go out at 50k!

 

the rear joints make noise like that too. can be tricky to really know if the sound is front or back best to check em all. That about the miles that my 3 went out.