When using an instrument soundfont in the Sforzando vst and playing certain notes, it makes cracking noises. Switch to the TX16Wx vst, and it only makes sound when you press the piano keyboard, but not when you play a midi track. Downloaded the Phenome vst, and also no sound when playing a midi track, but could see a blinking light in lane number 5. Turns out the notes on the track are going out on the midi channel 5. So check the notes on the midi editor by right clicking and Note Midi Channel if you're not getting any sound when playing a midi track.