intermittent grinding noise and trouble shifting

I have a 2000 Dodge Ram 2500 Van.  We haven't had it long, but bought it off my in-laws.  It has about 186k miles on it, and the engine was rebuilt and transmission replaced around 100k miles.  Recently it started making a grinding or grating noise which sounds like it is coming from the front end.  I had been driving on a highway (about 50 mph), got off, went into a parking lot, dropped off a passenger, and when I started driving again heard the noise.  It was NOT only when braking or turning.  When I came to a stop, the noise stopped.  I shifted to reverse and did not hear the sound when driving in reverse.  The sound has happened a few times since, but it comes and goes.  One time it became very loud, but again the sound stopped when the car was not in motion.  I shifted to neutral, and then back to drive to see if that would affect it, but the sound continued when I started driving again.  Then I shifted to reverse, and the sound was gone.  The sound is very intermittent.  Later the same day, while trying to replicate the sound, I also had trouble shifting.  The shifting problem has happened a few times since.  I'm accelerating after stopping at an intersection, get up to about 25 mph, and it won't shift; I let off the gas, slow down a little, then hit the accelerator again and it shifts fine.  This morning I had the noise again once, and the shifting problem one more time.  Seems to start when accelerating from a stopped position, and only happens when moving forward, but don't have to be turning or braking.  Don't know if the noise and shifting trouble are related.  Made an appointment for the local garage to check it out, but not sure if they'll be able to replicate since it is very sporadic.  Any thoughts?