I have a dodgeram 1500 v8 5.9l year 1996, when I start the engine I hear a unknown sound in the transmission, but when I put it on D or R I hear nothing, can anyone tell what's the problem is:(:(

How do you know that the sound is from the transmission? You could have worn motor and/or trans mounts which are shifting once you change gears, causing the noise to change or stop altogether. What kind of noise is it?