That could be a gasket leak on the bottom of your gas tank. This happened to me while i had a couple of Gxs-r's over the years, from a 600cc to a 750cc and apparently, this is pretty common in this type of bike, Do you fill-up fuel to all the way up to the very top of your gas tank? if the answer is yes, then this could be it. Take it the shop and see how much it is for the wrench heads to charge you...it shouldn't be more than a $100.00 parts & installations included...