Welcome Gene and RedRobin, Usually see you guys over in MK5Golfgti.co.uk. lol
I have an AXX engine in my GTI. Almost 3 years of ownership. My Engine has been ticking loudly since I got it. With 60000km's on the clock. It's about to hit 100000km's.
From all the info I have gather in regards to this issue. I can only determine/assume it's either the Injectors or it's the chain from inlet to outlet CAM.
I have replaced the following - Plugs, Fuel Pump, Three camshaft Buckets. Still made no change in sound. I was always lead to believe it's to do with the injectors.
But it can however point to the CAM's.
I'm sorry it's not the definitive answer you where hoping for. But on a side not the BWA also has this problem.
My friend GTI has this, 3000km's into a new Camshaft bucket it had warn thru and destroyed the Camshaft and pump (APR pump too). So he ended up doing Cambelt, New CAM and fuelpump/camshaft bucket. His car has been quiet ever since.