2001 Ford F-350 V-10 Rattling in front
 

I have a noticeable rattle or vibrations noise coming from what seems to be under the drivers floor board. This rattle only occurs in the middle of the first 3 gears or so. When the RPM's are higher it goes away then when it shifts and I push on the throttle it reappears and then goes away again as the RPM's rise. Don't know if I have something loose that may be vibrating or if it may be something in the transmission. If anybody has any ideas or ever experienced this it would be greatly appreciated to know what it is before I take it in and they give me the normal go round.