Buzz in studio monitors

Hi, I have a pair of 12 years old krk v6 s2 studio monitors that are buzzing. Buzz is present with and without audio cable plugged in. Turning the input sensitivity knob does not affect the buzz, it is always present at constant volume. I have tried different power outlet, different power cable and the problem is still present. Any suggestions what can cause this buzz. Thanks.

Look for electrolytic capacitors that are bulging on top.

Thank you. I will do that. Is there something that can be done to minimize the hiss? I am aware that some amount of hiss inevitable in active monitors but wanted to ask just in case..
Thanks

Hiss can be caused by using parts that are not made for low noise audio circuits. Modern audio opamps have extremely low noise spec's, much better than old transistors. Resistors made more than 50 years ago produced hiss.