I had a similar event last year, likewise with a Modwright Pre paired with a Belles 350A ref (WITH the soft-start circuitry). After LOTS of discussion, we suspect the problem originated with the Modwright Pre, as after checking with Dan Wright, I found my unit did NOT have the latest muting/protection circuitry to block DC surges. Turns out, David Belles uses VERY LITTLE protection circuitry in the 350A Ref, which is why it sounds so great! Dan upgraded my Pre to include the latest circuitry (as well as upgrading to the tube rectifier), and David Belles replaced my amp. Both have been singing sweetly ever since. David Belles (and Bruce Jacobs, marketing) are great to deal with and will certainly take care of you. I would also speak with Dan Wright, and have him cross-check your serial number to make sure it has the necessary protection. The power and finesse of the Belles makes it hard to give up, especially when the problem may have lied elsewhere.