Well - I have just solved this tick. Took all of 30 seconds once I had seen a post here in FordForums actually. The charcoal canister purge solenoid was just touching the wheel arch steel & when it operated it was causing the tick which was only there when under light throttle. I don't know the conditions for operation but I expect that it doesn't operate at idle but all the rest of the time and when the engine load increased the torquing of the engine on the mounts meant it moved just enough to no longer touch the wheel arch. So I rerouted the tube to the intake manifold putting the solenoid valve hanging well in the air & it's gone!!!
Here's the inspirational post:
Weird Ticking Noise
Maybe that's your problem too RaTTus since you have such similar symptoms.