Metallic Ringing From A String When Palm Muting Low E (High Gain Only)

I recently picked up a new guitar (Yamaha SA 2200 Semi-Hollow) and I’m running into an issue I can’t figure out.

When I palm mute the low E string (open) I’m hearing an unpleasant metallic ringing coming from the A string. It makes tight rhythm parts sound sloppy.

A few things I’ve noticed:

•	I do not hear the noise unplugged.

•	I do not hear it when playing clean or with light overdrive.

•	I only hear it under high gain.

•	I’m palm muting across the bridge and muting all strings.

•	The noise disappears if I lightly touch the A string with a finger.

•	This does not happen on my other guitars using the same rig/settings.

Since it only shows up under high gain, what could be causing this?