thanks guys. Yes it is SOHC (602 2.5 liter) with 10 lobes and 10 lifters. I replaced 5 of them last time I pulled one of the cams (only joking - THE cam).
I think you're right - it is probably the injector not spraying exactly right, or the PC being carboned up - the car was spewing black smoke when I floored it at high revs.
If it settles down I'll leave it in, especially if it's not a damage to the engine issue. But it is the wife's car, and the quieter it is the happier she is, and the happier I am. You know how it goes....
At least I can now sleep easy knowing I've got the right number of cams and that they're not the problem.
However, if it ticks again I'll replace the rest of the lifters.