Car: Audi S5 2008 V8 4.2L
Symptoms: There is a quiet (but noticable) ticking noise which can be heard from inside the cabin when the car starts. It starts of slow (maybe 10 clicks/sec) and starts getting faster and faster (maybe 100 clicks / sec) and remains. It's sort of like a positive feedback loop. When I blip the throttle and let it idle again (to around 2k - 3k rpm), the clicking speed resets itself, and starts slow and speeds up.
It's not the direct injection solenoid valves
The noise cannot be heard above idle
The noise can only be heard from inside the cabin (too loud outside)
The noise remains after the car has warmed up