1986 J-code C20 suburban with a 400, dont hear it in gear, but if you free rev it, you get a metallic "knock" from under the truck at the front of the transmission, it isnt the motor, the truck dont have an inspection cover on it, the starter has also been hitting and missing here lately...i dont know if its not the starter engaging or just missing the teeth cause of the loose or broken fly wheel hub....what you guys think???

Sounds like your starter isn't disengaging all the way, allowing the starter gear to intermittently contact the ring gear after the truck is started.

Chances are, if you rebuild the starter solenoid per the sticky thread, you will not have this problem. Ensure that the starter engagement gear is in good condition; this type of activity plays hell on that gear.

When you have the starter out, manually bar the motor over, inspecting the flywheel for damaged/missing teeth.

You want to ensure that the bracket located at the forward end of the starter is nice and tight; a loose bracket will also cause intermittent no-start conditions.

the started disengages all the way, it just wont engage sometimes....take one or two attempts before the starter drive hits the ring gear and starts the motor....but the flexplate sounds like a typical cracked, broken, or loose flexplate when you free rev the truck....

Well, it's possible... But I guess I'd be more inclined to suspect something banging around on the front of the engine, such as a a harmonic balancer or pulley making noise...

its coming from the front of the tranny, i slid almost completely under it saturday and its definately from the front of the tranny......ill check it out tomorrow if i can get time......