I just picked up my 2005 zzr600 about two months ago, and noticed I can hear a light ticking noise at low RPM. I can't hear the ticking once the RPM's get up there, but that could be because the exhaust noise drowns it out. A buddy of mine said it might be carbon deposits on the valves, but the bike only has 2600 miles on it. I wanted to see what you all might think the problem could be and if it could be serious..... I don't want my engine or valve train getting screwed up for something that I could fix myself or have a mechanic fix for under $200.