Same problem here. I'm on dealer #2 and visit #8 or 9. The ticking sounds follow the RPM's. They only get worse as time goes on, I've been waiting a few months now for something to go boom. It sounds like a rusty, old pickup truck. The dealers keep telling me that they don't hear any sounds, and that it's just regular "valve chatter" from the engine. Still arguing with them...

From what I've read on here, the four common causes seem to be (not in any specific order):
1. spun bearing
2. lifters/valves in the engine
3. loose heat shield
4. cracked exhaust manifold