How do I reduce static background noise with Garage Band?

Hi, I am using a Roland electric piano and I would like to record some tracks to garage band. I have them plugged in together with a 3/4 inch plug and a USB. Between notes, when nothing is played there are a lot of soft buzzing sounds, like a mosquito and faint static. How do I get rid of that. I tried changing the gate and compressor. That doesnt work. Help! Thanks!