It's gotta be either the valves tapping, an exhaust leak, or the cam chain. Anything else would be highly noticeable.
If you had a borescope you could pull the airbox, throttle bodies, and plugs back off, then stick the scope down into the Intake holes and check the valves to make sure they're not bent. You can't see them without a scope though. Pretty cheap on Amazon. I purchased this one. Works really well. Always find multiple uses for it.
Outside of that, you said the bike runs good, so maybe try running it for a minute and locating the sound. I don't believe the the TL is an interference engine, so no worries about the valves slamming into the piston heads. Who knows, it may turn out to be a minor exhaust leak. Just be sure to record while you're doing, so we can have a longer sample to listen to.