I have a '80 K10 SWB where I dropped in a tired 350 to replace the broken 250(?). It has the 3 speed + 'granny gear' manual transmission in the floor. Recently, the transmission has taken to making an odd clunking noise when I shift into 2nd (either up- or down-shifting). It sounds for all the world like something banging on the little thin metal shield covering the lower half of the transmission gear where the tranny and engine meet. My clutch seems OK though (no excessive play), and I have little trouble with 'granny', 1st or 3rd gears. Any ideas as what may be the problem? I am hoping to rebuild the engine and tranny, maybe next spring, but don't have the $$ for it now.