Valve noise

[F6T]

G'day team,

Ever since I've owned my ute, there has been an occassion valve tapping noise for the first 3 to 5 seconds on cold start up. Has never really worried me. Sometimes it will go for months and not do it even on cold start ups.

Recently however, I have driven it on two occassions where the noise doesn't go away - at all! - and it sounds like *****e. Then it will disappear again. These last two occassions have been quite bad - it is very noisey and sounds almost like a really bad exhaust leak (but its not that).

Has anyone else had this problem - and is it something that could be doing damage if it continues on, rather than stopping after a few seconds like it used to?

If it needs to be fixed, can anyone tell me what is involved and how much I'd be looking at to repair??

Cheers gang.