2000acuratl

Ive just recently rebuilt the trans in my 2000 acura tl with 203,xxx miles on the original trans. i rebuilt it because i had lost third gear because clutch pack was ate up.inspected and cleaned everything nothing besides the third gear clutch pack was bad(return spring, retaining washer and clip). (filled the torque converter before installing it) i got the trans back in the car got everything hooked up, filled the trans with fresh full synthetic atf(same as i soaked the frictions in). i started it up in park, no noises and sounded good, went to reverse still good, and then went to all the other gears and everything was good, BUT when i shifted back up and got to reverse there was a chincy grinding noise so i threw it in park and it was still doing it, i put it back into neutral quickly and it stopped, ive double checked everything and cannot figure out whats going on. does anyone have any idea what i could have done wrong or if a solenoid or something went bad, i really do not want to pull this trans AGAIN.