Is one of my tracks being stretched out? Rhythm not hitting beats as recorded.

I am trying to get ab general feel for a song I have written. I have laid down a basic drum track. Now I am recording rhythm guitar on a separate track. The problem is that though I know I am hitting the beats in time, when I play back the result, the guitar seems to become increasingly out of step with the beat as the timeline progresses. Are there settings which have stretched out the second track slightly? It's never happened before and now it's happening all the time. I don't understand it.   

Just to add: 

After recording all the peaks look correct on the graph but when I take the time line back to play it the rhythm graph looks different (It changes).

I also don't think it's a mic/playback/driver issue as it's not just a record or playback delay. The discrepancy in sinc gets steadily worse as the track progresses suggesting to me that it's a minute 'stretching' of the track