This is an area of GI research that is poorly understood and frequently called "no man's land of gluten sensitivity". There is some evidence from small clinical IBS studies that show there may be a non-celiac gluten intolerance but there are no clues as to what might be the cause.
One of the best studies to date is the one given in the reference below. It was done by some of the researchers that developed the FODMAP approach (see references in my signature).
There are no tests for non-celiac gluten intolerance other than try a gluten-free diet. However, there is a confounding factor. Some people have difficulty with fructans, a FODMAP, found in wheat which also contains gluten. Sometimes it is useful to first try removing wheat products reducing fructan consumption before trying a full-fledge gluten free diet which is more difficult to follow.
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Re: Can Gluten Cause GI Problems If You're Not Gluten Intolerant?
