I have a 11126 Legacy Big Boy I purchased used recently. Tender suddenly started putting out loud white noise in place of engine sounds, though, if you listen very carefully, you can hear the engine sounds are still there. All other operational functions work - just corrupted sound. Found I could fix (in my mind, a temporary fix) by gently pushing down on the volume control knob under one of the tender's hatches. I suspect one of the pins of the volume control pot is shorting to the tender body.
Haven't had time to take the tender body off to investigate, but I wanted to check with the forum members if anyone has experienced this, and what the member did to fix.