What type of underlayment did you use???  I know you said your on a crawlspace that is insulated...but is their a moisture barrier...these are things to consider.....

One thing to know is when installing this flooring make sure when knocking the ends together not to knock them too tight or there will be too much pressure pushing the boards upward. After going down that run knocking more together you end up with boards that are waiting for the right moment later to start rising upward noticeably. It's normal for boards to shrink which would cause a problem. Imperfect design is what i say.