knocking uh ohhhh

for the past year, ive been hearing a knocking sound in my v6 89 RS. 2.8, the wierd thing is, i would shift from first into 2nd, then 3rd, then from 3rd into 4th i would hear one big knock, but the car runs great. lately the RPM gauge has been inaccurate, and jumping around alot, and at start ups the oil pressure gauge jumps. but its been chugging alot during the take off, and when i flore it. i hear a sort of rattling sound, but not from the top, when i bend down and look under the car, the sound is clearly louder and more notticable from under the car. does anybody know what this could be caused from? hopefully not a rod or main bearing,

the car has 97 thousand miles, ODO hasnt rolled over.

-- edit --

the knocking sound sounds like it could be going as fast as the crank