When I plug in my headphones, a static hiss comes out of the internal built-in speakers below the LCD on the mini 9. There's no clicks or beeps, it sounds just like white noise or AM radio static, and it's about as loud as a spooled-up cpu fan would be on an average notebook. The speakers work fine for playing audio when the phones aren't plugged in, and the headphones sound fine when playing audio otherwise (with no significant hiss coming from the phones themselves, only the speakers). If headphones are plugged in at boot, the hiss only starts until after OS X has started up.
Thanks in advance