Ok, so I removed the valve cover to change the gasket (annoying job, especially that one nut underneath the wipers which is impossible to access) and the old gasket was crap (as expected). Cleaned everything up and changed the spark plugs to new platinum ones and put everything back together. The ticking noise wasn't as pronounced but it was still there which was strange. So then I had the bright idea to check my oil level (I'm sure most of you here probably thought: "the guy must have already checked his oil so I won't even suggest it") and it turns out I was quite low on oil (strange cause I checked my oil level a month ago (less than 1000 kms) and it was fine. So I added some oil and some Lucas oil stabilizer (the engine has 268k on it) and the ticking noise went away.
I have no idea where all that oil went cause I'm not burning oil (I'd see the blue smoke) and I don't have an oil leak under the car...weird...anyway, I'll need to keep a close eye on the oil level to see what's going on.
So in the end, although changing the valve cover gasket and going back to platinum plugs helped, the real culprit was low oil.
Thanks for all your help guys!
Currently own: 2006 Audi S4 Avant 6MT
Previous: 1992 325i