Q: There is small glitch noise happening every couple of chords or so. Even with and without headphones plugged in. Can someone please help!

It could be several things. First, check buffer settings in preferences. Adjust to achieve the optimum balance of performance and latency. How much RAM is in your machine? What processor is in your Mac? Also, if you have other apps running, close them.

I agree with Lifenoise's implication that what you're experiencing is likely due to your MainStage settings not being configured correctly. What is your buffer setting?

Looks like you found the buffer settings. Try boosting the buffer size to 256. Also, try turning on the I/O safety buffer.

Is it like a click? Is it on both channels, left & right or only on one side?

DaCaptain