Well I didn't crawl underneath to do all the checks as the noise was gone friday morning. Aaand it was ****ing down the last few days I was in Ireland so I didn't feel like crawling around in the mud to look for something making a noise that wasn't there. I didn't feel movement in the crank pulley btw, but will check this again properly with a larger pry bar. I didn't have the other symptoms of a bad flex plate but will pop the inspection cover and have a look as now I don't trust it anymore... However my gut feeling is pointing towards something exhaust related.
Another reason that I didn't further investigate after the noise went away is that I have a recovery insurance and I found out it requires a certified roadside assistance company to declare that the car is not driveable --> I needed to break down with symptoms... Recovery on my own initiative to be cautious would probably have cost me a new engine in total. So if you know there's something maybe not right you have to drive until it breaks. Ah insurance companies love them!
I'm happy I could complete my trip and thankful for all the input here! That's what makes this site great! Now time to get the car on a lift and get to the bottom of this!
Anyway, thanks for all the input here! That's what makes this site so great! I'll give an update on my findings.