please help!!! went out on my bike the other day,i get the usual tappet noise,but noticed every so often a 'metallic' knock,it only seemed to happen in top gear cruising about 50mph,cant exactly tell where its comin from but its very intermittent.i checked the oil which was very low,so decided to replace with a new filter n oil,i'm terrified now that the engine has been damaged,but surely engine damage noise would be there all the time. the chain was loose at the time ,so i've sent for a new chain and sprocket set,hoping its just chain noise.havent run the bike since, but would appreciate any ideas what this noise could be. n.b checked the oil filter ,there were no metallic particles in it. p.s new to this forum,seems the best place to get advice and stuff,cheers dudes.