More than likely it is the clutch release bearing also known as the throw-out bearing. You should be hearing it to some degree in all gears. It is likely worn out. You should probably replace the clutch also since you have to remove the transmission to get to it. All 3 speed and 4 speed transmissions have a fill plug on the right side of the trans case.
Fred

Last edited by rfs56trk; 04/17/2010 9:42 PM.

1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine