Couldn't tell you, if that is it, it may be a small piece of threaded rod that wasn't glued properly, or if no rod used, something wrong with the wood tenon at the joint. You really need to contact the cue maker to see what they think it is, and if it is worth fixing given the price range of the cue. Are you checking for the sound with the shaft on? If so it may be the ferrule on the shaft even though you say it's the butt area.
I would contact the cue maker and not wait till the next expo. A reputable maker would want to make that right. Just call them up and see what they say. That really should be the first thing to do.