Fan belt squeling

Hey just wanted to know how to get rid of some annoying squeling noises comming from the fan/drive belts. I've already tightened the tension of the belt it has made it better but its still there! What can I do to fix the problem. I drive a hyundai sonata 2000. Also the battery wire which drives my stereo is not working. How can I fix this, I checked the fuses but I can't find the problem! The car has done 150000km. Thanks