94Z286SPEED

i have searched and tried all the tricks is it real knock? i start the car and it runs perfect for ten minutes then the knock comes. then it will go away for awhile then retutrn. tried running 100 octane but it still comes and goes. i tried tapping the block to see if the sensor works and it shows knock when i tap it then goes away when i stop tapping. could the sensor it's self be bad if it knocks when i tap. i have the lt-4 km could that be the prob?

Any help would sure be appericiated, i'm about ready to give up on this chevy and go to the darkside!