Dave,
Do you have a nocking point above and below where you attach the nock to the string? If so, maybe the points are pinching the nock and making the arrow rise up when you draw. Could also depend on your hold or placement of the release if you are using one. So I guess I need a little more info...Do you use a release? Do you have two nocking points? Is the string really tight inside the nock? Does it keep doing this with the same arrow or does it happen occassionally with all your arrows?