I have the exact same noise on my A3 2011 but I do not have any of the bad symptoms such as loss of power, car struggling to start etc...
I decided to bring the car to a Diesel specialist to get the car diagnosed and have piece of mind, they checked the pump by removing the head and didn't find any metal bits in the pump neither on the head (they even used a microscope for the head), they also checked the readings with their software and all reading seemed to be matching requirements, the only thing they have found was that the fuel filter has not been changed since 2013, changing the fuel filter didn't remove the noise.
One thing they told that was interesting was that they disconnected the plug from the pump head and the noise was gone (doing so will introduce a error code), so they tried to fit a new head on the pump but the noise came back so that got them confused as they have seen that and can't really fault the car, they said to me that I could change the pump if I wanted that would an expensive bet as they are not even sure it will cure the problem (if it is a problem).
So I guess what I have learnt from that is that a ticking sound coming from the high pressure pump does not mean you are in the worst case scenario, as I can read here some people just drive with noise and doesn't seem to cause any issue, as for me I have decided to drive the car a bit longer and see if the new fuel filter could potentially cure the problem ( i will this thread updated) , on the other hand I will keep googling for answers.
I could potential replace the pump but we are talking about £922 + 20% VAT (that is pump (£422 + VAT), cambelt and labour)
Almost forgot, another thing the guy from the garage suggested was to bring the car at Audi for diagnostic as he said that the pump head communicates with the sensor on the fuel rail (which made me feel better as the pump the noise was gone when disconnecting the plug from the head, which means there is nothing wrong with the internal pump components movements as it is driven by the cambelt) and that it might need a software/firmware update but I am not too sure about that, knowing Audi they will just try to take as much money as they can from you and tell you to change the pump.
I hope it will give you guys some more info and I wait for your comments