I hear a rattle when .........
 

I have a 01 slk320 (<20k miles) and I hear a rattle when the automatic shifts from 2-3 the first time after start up (sometimes it will do it the second or third time it shifts up)...... the sound is one that reminds me of a metal plate spinning off balance and shaking. Anyhoo.... does anyone know what it maybe? ....is this yet another "new" issue? or one that is well known? Thanks so much, WW.