Auto Transmission - grinding when in gear

Hi guys, had my suzuki swift (aveo) since 2004, and just recently started getting some problems.

If i turn the car on and warm it up for 5 minutes, shift into gear, everything works dandy.
If i turn the car on and right away shift into gear, i hear grinding noises coming from the engine until i accelerate, the noises stay for a few minutes if i slow down until the engine warms up. I checked the tranny oil level and it seems fine. Anyone know what might be wrong?

thanks a lot!!!