Center force clutch noise

my friend and i put in a new CF dual friction clutch, throwout bearing, pressure plate etc in my 70 duster. It has been fine for 700 miles. Now when I let out the clutch I get a small "groan" at the bottom of the clutch as I let it out. All else seems fine, grabs, and shifts good.
Any ideas where this is coming from. Only in 1st or reverse, not when up or downshifting.
thanks
Mike