BAT VK5i Issue

When I put the unit in Mute I hear a very loud thump from the left speaker and the drivers momentarily move in and out a significant amount. This just started happening. What can be some possible issues? Thanks,
Check with Bat I had the same issue with a 51se turned out the caps needed to be replaced.
The caps needs replacement, the sooner you do it, the better as this can kill your power amp and your speakers as it gets worse.
how can that harm an amplifier?