MK2S X axis(?) makes strange clicking noise  

MK2S X axis(?) makes strange clicking noise

[Edit] I posted this in the MK2 forum at first, but as this was built from a kit I figured it might be more appropriate here. I'm not able to delete the post from the MK2 forums, unfortunately.

I got and assembled my MK2S kit yesterday, and within a few hours had it calibrated rather well and have been producing some nice prints. I'm not sure when it started, sometime late last night, but during my last few prints I've noticed a noise that seems to be coming from the X axis motor or in that general area, but I can't seem to pinpoint the source of the sound.

I described it as a "clicking" in the post title, but this is not a noise I would associate with a bad stepper motor. It sounds more like the teeth on the inside of the belt are running over something and I'm hearing the thump of the teeth on whatever it is. However, nothing seems off after investigating. Furthermore, this sound doesn't seem to happen all the time. During initial calibration, the sound is absent. Even during the print certain movements involving the X axis will have it, while others won't. The print quality seems unaffected by whatever's causing the noise, I haven't noticed any slipping or anything that would indicate any print head movement being affected.

I'm trying to get a video that clearly demonstrates the sound, but without knowing where it's coming or what's causing it it's hard to anticipate when it will be the most audible. I'll keep working on that; if there are any other questions that I can answer to help narrow things down, please let me know.

[Edit 2] Here's a video; the noise is a bit quiet but it's the best I could do. Especially noticeable at the end.

Any and all help is appreciated. Thank you!