iMac sound problem. Help!

[mattioch]

I bought two studio monitors and I have them going into the headphone jack but I keep getting static sound from my speakers. I don't get the same static from a MacBook Pro or my iPhone. I need help! Should I take it to the apple store to get the sound card checked?

 

[PerformaGuy]

Is the iMac grounded? The three prong plug should connect directly into a wall outlet.