Hi Tony,
Most frustrating for you.
If you have a PC or Mac could I suggest you turn on the B2's NAS and listen to its music that way using a PC or MAC app to play. This will tell us if
The problem is with the B2's music files themselves or with the hardware/system the B2 is using to play this music.
The other possibility conformant with what you describe could be a software corruption with the Brennan software which is stored on the B2's SD Card. You could test this by replacing this card with a new one from Brennan or re-flashing the software on the current one.
Fred.