common problem. probably just need some new shocks. but check to make sure the shocks you have now are installed correctly before you do anything. a while back i had to get some body work done which involved taking the hatch off and when i got it back it wouldn't stay open. turns out they installed one of the shocks backwards so it wasn't extending all the way. and they wanted ME to buy new shocks($$$). needless to say they felt like retards when i brought it back to them and showed the pros how to fix it.