tranny problems?

[<girault@bellsouth.net>]

My 70 1600 has started making a loud clattering noise when I let off on the
gas and start coasting - like to a traffic light.  It stops immediately when I
mash the clutch.  It sounds like a u-joint going bad but I checked them both
and they are tight as can be.  I also suspected that the tail pipe was
vibrating against the frame where it goes thru the hole in the frame, but I
wrapped it with a rubber gasket and it still does it.  The only thing left is
a gear going bad.  Any opinions?