2000 Subaru

Engine problem
2000 Subaru All Wheel Drive Automatic 76,000 miles

My 2000 Legacy Wagon has a 2.5L engine with an automatic transmission and has an engine vibration when the engine is cold, transmission is in drive and at a stop. No vibration is present with the transmission in neutral or in park. Once you accelerate the vibration appears to go away. Once the engine is fully warmed up and in drive (at a Stop) the vibration is negligible. Placing the AC on doesn't seem to affect the vibration in any transmission settings. Any suggestions as to the culprit? Engine mounts?Otherwise the car has not had any major problems. Thank you.
Frank