Sometimes there's a buzzing noise when you have a crap ton of distortion in use. Usually, you'll have to listen closely when the track is 100% silent or change the "main output meters" in the top right to the 144dB range to see it (by right-clicking it).
If you hear it, then slap a gate on the devices you used distortion on (or on the main output of the draft) until it's gone.