Recently got a used custom 22 and noticed a strange oscillating hum noise coming from the lower strings when they ring out. I play through overloud th3 on my computer but I tried another guitar and could not reproduce the sound so I'm pretty sure its not the audio interface/studio monitors/cable. The hum noise is only noticeable when a note rings out and happens with both pickups although maybe more so with the bridge. Any ideas what could be causing this oscillating hum?