Gh0st

Good evening, I've recently bought a Les Paul Studio from the 1997, great one, full mahogany body, ebony fingerboard, klusson tuners, equipped with pafs... Though, I've noticed that when I plug in my rig (Vox v845, boss sd1, vox vt100x), when the bridge volume pot is set from 5 to 10, when I mute the guitar, it makes a strange noise, similar to a whistle. I thought that live it would have been gone, but still... Does anyone know something more about it?