Many thanks for your reply.
I've since discovered what the problem is.
I have discovered that when you stretch a sample to fit a new length, Cubase FADES out the sample at the end! Not only that, even tho when you drag the sample it 'snaps' to the grid, when you zoom in, you can quite clearly see a gap between the end of the sample, and say, the bar to which you dragged it to!
I didn't hear the clicks when I played it back because I had the METRONOME on. BUGGER!
There is no easy way around this. I've tried using Ableton but it's confusing the hell out of me and i don't have time to sit down and read a manual right now. So I'm going to spend a good hour tweaking the samples in a separate audio editor to iron out the gaps and keep them the same length.
Thanks again for your reply. If you do have any suggestions on how I might avoid this happening again (i.e. not using cubase lol) then I'd be keen to hear