Logic Pro; click noise after every audio loop

Hey all- first post.

I searched to see if anyone has a similar issue as mine and I found someone who did, but no one answered. Using logic studio, I have a mac pro 2.8 (early 2008) with 8 GBs of ram, an apogee duet, and a yamaha motif that I use for midi and audio recording.

Say I record an audio loop that is 4 bars. When I go to repeat that loop a few times and play it back, at the end of the loop (every 4 bars) there is a click or pop noise. I figure it is probably something simple.

I am obviously a noob at this recording thing; I am slowly prodding my way through the logic studio book. But I could use some help with this pressing issue more immediately. I figure it has something to do with the levels at which something in my chain of gear is recording at, although I tend to get confused with this and if I just start changing levels on my own I'll probably end up messing something up.

Any help and advice is most appreciated, go manny pac!