The normal way to loop a clip is clicking the loop button and then dragging the end of the clip (in the timeline) to whatever length you like:
http://manual.reallusion.com/iClone_7/ENU/Pro/Default.htm#iClone_7/Pro_7.0/09_Animation_Timeline_Editing/Speed_Loop_and_Blending.htmIf that is what you're already doing, then you can try blending two identical clips (same page of the manual). You can try tweaking the length of the blending section of the following clip (drag the front of the clip to make the blend section shorter/longer). And you can also try with varying distances of when the new clip starts. It doesn't have to be directly against the previous clip...but the blend section should be against or overlapping the previous clip.
You can also try breaking the clip. If you find the exact point where the clip will loop without any weirdness, right-click on the clip (on the timeline) and select Break. It will break the clip into two clips. You can delete the second part and try looping the first part (if you cut in the right spot).
- Keith