Finally found it, but how do I stop it?

[JayWalkingBlues]

So I've been vexed by a vibration in my Alvarez Parlor guitar for the last few months. I thought maybe a loose brace, checked them, no problems. Thought maybe the wiring, wasn't that. Thought maybe it was fret buzz (although I never really thought it was). Everything on this guitar was as tight as the day I bought it. Finally, last night, on a whim, I removed the battery. Instantly gone! The battery is in a separate location from the preamp.....nearby the bottom strap button. The battery and plug are the same unit. The 9v battery fits into a sleeve, then slides into the jack board....similar to this: https://www.aliexpress.com/item/NEW-...302932557.html
Do you guys have any suggestions on a good permanent fix for this? At this point I don't know if the sleeve is vibrating in the housing, or if the battery is vibrating in the sleeve.

[Quickstep192]

Just a guess, but I’d think a small piece of foam to keep things still might do the trick.

[Ned Milburn]

Originally Posted by JayWalkingBlues

So I've been vexed by a vibration in my Alvarez Parlor guitar for the last few months. I thought maybe a loose brace, checked them, no problems. Thought maybe the wiring, wasn't that. Thought maybe it was fret buzz (although I never really thought it was). Everything on this guitar was as tight as the day I bought it. Finally, last night, on a whim, I removed the battery. Instantly gone! The battery is in a separate location from the preamp.....nearby the bottom strap button. The battery and plug are the same unit. The 9v battery fits into a sleeve, then slides into the jack board....similar to this: https://www.aliexpress.com/item/NEW-...302932557.html
Do you guys have any suggestions on a good permanent fix for this? At this point I don't know if the sleeve is vibrating in the housing, or if the battery is vibrating in the sleeve.

I have added masking tape to a 9v battery that was vibrating in a Taylor battery compartment to good effect.