Dear and beloved car talk fellows, my name is Nick and we have a 1998 Subaru Forester with a 5 speed manual transmission.
When the car is stopped upon accelerating in first gear their is a thumping noise with diminishes after the car reaches second gear. There is a thudding vibration felt directly to the right of the driver underneath the car. The thumping would be where the drive shaft would be connecting to the rear of the vehicle. I cannot see any universal joints as the drive shaft is covered my the exhaust system.
Could it be a U Joint? The CV axles are all intact and the boots are undamaged as well.
Check for a broken motor-mount which will allow the engine to flop around…