disco td5 diesel knock

hello every one ive had diesel knock now for a while how can i exsplain it when its warm normall running temp it does it rev the engine and let the revs drop and it holds just above 1000 rpm and knocks and thyen idles normall . not in gear i let the arm brake off to free wheel and the revs go up slightly and it knocks. the engine juggles and knock but when you come to a stop it idles normall and knocking stops cant under stand what makes the revs go up on its own changed cranks sensor as have had it plugged in and was told to change crank sensor so done that no change still there the had it plugged in again and they done cylinder balance and they are all going mad from -1 then jump to -19 to - 20 and they are all doing it from cylinder 1 to 5 no oil in ecu or plug now ive been told to change injectors as one or two maybe going wrong any ideas or help would be graet thanks ultra 150