Bad news. I recently had the balance tube off and accidentally knocked some water into the plenum (don't ask how). I thought I had got it all out and refitted the balance tube. I then started the engine and it blew a bit of steam out and black muck out the exhaust and then ran OK. However, the engine then developed a loud tapping sound at the rear of the plenum (ie at the top of the engine). The noise rises and falls with the revs. The engine seems to run OK just with this really loud tapping/ticking noise. I put the stethoscope onto each injector and heard them all OK except for No 6 which seems much quieter. Again, though, the engine is not running rough. What could be causing this loud tapping noise? Could one injector be affected by water? I don't want to drive it until I know it won't cause further damage. I don't believe it is lifter noise as I can't see how any water would have gotten across to the oil. Please help!