I get a strange tapping noise from the engine, runs fine and only noticable while idling sound is like a finger flicking your chin, and appears to be coming from under the gas tank cover, my friend swears it's a bad rod, but spending hours on youtube with videos of bent rods or valves sounds nothing like it, esp since the sound is completely non-existant or unable to hear it while revving or riding all day everyday. my friend also has the exact same bike, and while revving and riding ours sound identical with his minus the tapping sound on idle. (which isn't always there btw, pretty inconsistant)

The bike sat for a while before I bought it and it had a tank full of rust, I haven't had chance to change the spark plugs yet but ran probably about 8 ounces of seafoam (in the tank) within 3 fill ups and runs great now

before the motor stumbled and rode rough few weeks ago only after a long ride (haven't had problem since seafoam) when it'd studder I'd just pull over hold the clutch and rev high a few times and it'd just be fine. I'm guessing this is cause of bad plugs since it was ran on pretty bad gas for a week before I got around to it. (gas tank was covered in rust enough to change my finger orange if I rubbed it on any given point)

I don't know if the problems are related but noting it just incase.

 

i'd say it's the valves you may want to get them checked but most bikes do that especially since you say it's under the gas tank cover (valve cover) I know the valves tap on my f4i

 

Well, I just flicked the bottom of my chin. I think it sounds more like an air leak somewhere than valves or a bent rod. Air leaks will tick with the engine rhythm. Check the simple things before digging in the engine. I don't know the history of the bike, but valves on an 04 really shouldn't be out of spec, and a bent rod rarely just "happens".

Definitely get around to changing your spark plugs. You may want to check fuel filter and injectors as well if you ran a very rusty tank for any amount of time.

Good luck