Easy way to eliminate the clutch as the culprit which usually it is, Is shim one shoe as shown in the image below and does the knocking (clacking) go away.
If it goes away you found your source of the knocking and if it is still there then look for other possible causes.
(1) This is a new clutch so I was only able to fit two pieces of paper between the shoe and the tower sliding surface.
Used clutches just keep on folding until you can't fit anymore and you only need to do this to one shoe not all three.
After the paper is as tight as you can get it start the engine and did the knocking go away or is it still there.
Gone away = clutch
Still there = keep checking elsewhere.
DO NOT use ANY metal feeler gauge or any metal period as if it decides to fly out and it picks you to attack it could be a eye or friendly shrapnel.
If you are standing there by it WEAR your SAFETY GLASSES!!
