1994 mercedes benz sl600 dinging noise??? help?

have a 1994 mercedes benz just bought it. it has the hard top and if you take it off it has the soft top under it. but the only thing, it makes a dinging noise like the door is open or the top isnt on all the way. i checked all the latches and everything but it doesnt go away. when you have both tops down it stops. any idea on how to fix it??
 
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