Prusa i3 x-axis drift (no replies)

Hi all,

First post on here - I've been soldiering on by myself till now, but this one has got me stumped.

I have made a Prusa i3 single plate (aluminium) and have been getting ok results until the last week or so.

I keep getting this random drifting of the print on the X-axis (the one attached to the z-axis in case I have got it wrong). A print can be going fine for and hour and then just start to drift off by 2-3 mm, then it tends to hold for a few layers before starting to drift further.
My belt is tight and I'm positive that it's not jumping a tooth. The motor is hot, but I can still hold my fingers on it, so it's not burning up.

The electronics are pololu from Tony Lock and have been spot on so far.

I have tried 2 computers, a windows 7 laptop and a macbook - both running repetier and using slicer.

Both slicer graphics look perfect on screen - the numbers look good in the code - the drift has got to be somewhere else... It's driving me bonkers!

I have mainly been trying to print the parts for richraps 3dr, but other files have failed too - it's not the STL files I'm pretty sure.

If anyone has any ideas, I'd love to try them - I think I'm running out of steam :-)

Cheers,

Ian