I was just having a fettle and noticed that the headset had come slightly loose (slight knocking when rocking the bike on the front brake). I tightened it up and eliminated the knocking but noticed a really dangerous sounding rattle. It happens if I tap on the bars, or bounce the front wheel on the ground whilst holding the top tube. I can't pinpoint where it's coming from exactly but it sounds dangerous! Needs sorting pronto as I'm down to this bike only at the moment Any ideas? I'm thinking maybe the headset bearings are shot?