After thinking that I've somehow fixed the ticking noise a number of times and never really knowing why I came across a page that said to rev from idle in neutral slowly to 3000 rpm over 15 secs and then letting it drop back to idle and keeping it there for 15 secs and repeating that cycle (up to 30 times apparently) it'll come good.

Ok I did that a couple of months ago (took about five goes) and it seemed to work.

Started to come back a couple of times since and both times doing the above made the ticking noise go.