Agree to call SMc Audio in any case to discuss the amp's history. But I believe the seller of the amp is stating in his description that when he had the Gold upgrade performed part of the upgrade is to take out the mechanism that prevents the thump in favor of better overall sound.
FWIW, my DNA-1 Rev A has the harmless thump on power up.
I had SMc do some upgrades in 2014 where it was also fully tested and "ready to go", while having the thump, they didn't mention it. The amp has worked flawlessly for me for years. I'm not too concerned about it, I leave the amp on most of the time anyway.
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