Sounds like you have a leak. Is it a glass top? If so you may have leakage around the edges. Check the accessory forum for the thread on sealing the glass with silicone. You can also check for leaks by opening the top about half way and letting it go. It should not slam shut, you should hear a "whooshing" sound as the air escapes evenly around the edges. you can seal the top edges by using painters tape around the top.
