hope your ready for this but it is a job you have to pull the whole steering wheel off take out the turn signal switched and behind that you ll see the ignition switch there is a small hex head screw that holds the ignition in it might be loose i had the same problem
the knock could coe from a few places, if it is in fact a "knock" it could be a piston rod, if its more of a tapping comming from the top of the motor you could have a loose rocker arm, if it is a loose rocker arm i would suggest tightening them up if it stops and comes back i would replace the lifters
If the steering wheel on a 1990 Chevy 2500 feels loose, one or multiple bolts may need tightening. Threadlocker might need to be applied to the bolts to prevent them from coming loose again.
If your 1981 Chevy V6 it leaking oil you can try simply tightening the bolts if they are loose. If that doesn't work then replacing the gasket is not a big job.
Bad relay? Loose connection?
Seized engine Discharged battery Loose or corroded battery cables Starter or starter solenoid Neutral safety switch
Your shift linkage may have slipped or become loose. Check your linkage.
Finalize
I just had this problem with mine, and it was a loose nut on the linkage. There is also a brackett held on by the transmission pan bolts, they were loose too. After tightening all these up it shifts fine again now.
At the base of the distributor, there is a tab, with a bolt in it. Tightening or loosening this bolt, will do the same, with the distributor. The distributor, by the way, times the motor, so, you will need to retime it.
There are two large bolts which hold your starter to the block. you can try tightening these or a better idea is to go to your local parts store and pick up a couple of shims. Stick them in the gaps and then tighten the bolts down.
yes you have to pull the steering wheel off, and becareful you don;t loose the spring.
take out the glove box, lower panel, under glove box and first to disconnect the heart hose, loose the lower panels, loose some bolt turn the core clockwise .pull it out