hi when I put my 94 full size blazer w/ 4wd into gear it starts making a loud knocking noice and if i hit the gas and speed up it turns into a grinding sound what could this be?

Optional Information:
1994 Chevrolet Blazer K5 350 TBI

Already Tried:
the noise seems to be coming from the flywheel/torque converter bell housing area but not completly sure it started out only making the noice in reverse but now its gotten worse and does it in drive also...sometimes even park I can still drive the truck but the noise will start and i let off the gas and it will go away for a while