I recently swapped a lower miles engine in to my 02 gtp motor was from a 98 gtp. When you first cold start the car i hear this slight grinding sound coming from the bellhousing area. It will last for about 30 seconds and you can hear it fade away. The sound is gone for the rest of the time. Its really just that first 30 seconds upon a cold start. The car sat for about 6 months between getting the old motor out, finding a donor, and installing the newer motor.
I changed the transmission fluid and filter when i did the motor swap.
Someone i talked to said maybe that starter is sticking. But, like i said it only does this on a cold start.
Maybe a torque converter issue? I'll try and post a video of it later.