If your '36 GMC is like my '37 Chevy, the crank bezel is loose, situated between the door panel and crank arm. My truck makes so much engine noise and transmission whine, that I don't notice any rattles.
Kent

1937 Chevy 1/2 ton
1942 Chevy 1/2 ton
1947 Diamond T Model 509
1951 Chevy 1/2 ton
1950 Chevy COE Model 5700 ~ "Barney" ~ And more pix