I have a similar recurring issue but it doesn't come back. I've described as hitting the "shit switch". Everything's fine, volume up, rarely a slight flicker of yellow clipping (manual says OK)and amazing sound. Treble boosted a bit much, then "shit switch". Both speakers sound like crap. Replaced tweets, cut boost in 1/2, barely boosted. Ran same album twice (I'm a dork) good volume sounds amazing. 2nd run on that album, turned volume down a good bit. 1/2 way through that album... "shit switch" again. I wasn't even pushing it. No knocking or ratty highs or any sign of stress. Frustrated

B&W is famous for playing extremely loud without distortion. Check them out.