I've noticed a rubbing sound on my Canondale Synapse the last two times I've ridden. The sound usually occured while putting load on the crank (usually going up hill). This afternoon I checked to see that the rear wheel is tight and noticed that although the wheel appears to be secured (it takes preasure to close the quick release) the wing nut on the opposite side of the quick release turns freely. I assume this isn't right and I'm worried the bike may not be safe to ride. Am I right? Is this something I can fix myself? Thanks in advance for the help.