I rebuilt my 96 accord automatic transmission. I replaced all O-rings, the filter, the frictions and steeles, the gaskets and the sealsaround the input shaft and the differential. I also replaced the torque converter and the o-ring on it.

I start up the car and it makes a grinding noise in park neutral and reverse. The grinding noise stays sometimes and goes away after about 45 seconds. In drive the sound goes away completely. All of the drive gears work fine with no grinding sound

Does anyone know what could be causing the problem and how to fix it?

 

Verify CV axles are installed all the way.
Verify correct amount of fluid is in the sump, prime each gear P>1, put back into park, pull dipstick, wipe clean, reinsert and verify it is within the hash mark. With car on level ground.
When the trans was disassembled, how did 4th gear look?
How did the shift fork look?
Reverse gea condition?
Any abnormal wear or swirling on any other components?

 

All the gears are good with no abnormal wear and all were primed with full fluid level. With the transmission out I can spin the input shafts it's no grinding. When the car is lifted on jackstands in neutral it does the grinding when I spin the wheels which leads me to believe it's the cv axles. I verified that they are seated properly and had a couple friends verify as well. Is there anything I'm missing?