typically, its not just noise u hear.. here is how most of it goes. the valves generally DO NOT loosen up over time. people have tendancy to think this, but its not case most of time(again not all time, but most) in one with 40k miles, what most people will see is that all exhaust vavles will be within spec, and prolly 1/2 or so of intake valves on tight side. tho most will still be in spec, maybe couple that are too tight. people hear vavle tick and think it needs valve adjustment..99% of time, thats not case. exhaust vavles are hardened for temps, intake valves are not, but still see same temps. over time and heat cycles, the metal will stretch(grow) so vavles will become tight. decrease in mileage, hard to start, poor idle can be symtoms of tight vavles. these vavle trains on these bikes are extemely tough. tho things do happen occasionally.
checking vavles is one thing...if they need adjustment thats another. just checking them, requires taking off valve cover and checking. if they need adjustment, that requires pulling cams out, finding out what shims on are head, and what shims u need. just checking valves and if they are good is prolly about 1.5-2 hours, actually changing them can be between 4-5 hours, tho it generally doesnt take that long.
my advice is get service manual, and at least check ur own vavle clearances. if they need changing, thats one thing, but 99% of time they wont. so its worth investment, getting manual and feeler guages and familiarizing urself with it.