1994 Pontiac Transport Car Makes Loud Noise Only Drive Slow Idleing Drives Fine

It may be a lot of thins. Does the noise change with engine speed. Say when parked and you rev it up, does the noise change? Or, does it only change when you srart moving. That will at least tell you if it is in the engine or is in the transmission or drivetrain. Try using a long screwdriver with the handle at your ear and use the flat blade or phillips end as a , "Stethoscope" to help you hear where the noise is coming from. It sounds like an odd thing to do but it really does work. Also, the next time you change your oil, look for metal particles in it. They willl be very small and settle to the bottom so use a very clean drain pan. Use a flashlight or get in the sun light to look for them. There presence indicates engine damage.