My corsa was a 2lt 16v and the engine ran fine no problems nothing, the engine was a minter pulled really well everything.
i took the car off the road in Sept '03 (engine hasent been run since then)
took the 2lt 16v out of my corsa and fitted it into another corsa last week, again she started up fine, ticked over fine and when drove she still pulled (havent given her to much as still bedding her in)

BUT heres the problem
there a kind of tap/knock coming from the engine at around 2.5k revs and gets faster when revs are rasied slowly BUT go's when rev'ed fast from 2.5k upwards

anyone have any ideas?
done a total engine flush,oil change etc etc

could it be the oil pump on its way out?