The strings need to be tightened. Not sure how yours are made, but mine, I can simply unscrew a screw from the wall with a "thingie" the strings go through, pull them tighter, and then re-tie the ends, making the strings tighter. The first year of ownership I had to tighten a couple every month or so. Then last year (second year), I think the strings have finally maxed out their elasticity and didn't have to do it all last year. This year, not yet either.