There'll be a few owners of DC blockers that must be wishing that they'd taken your cheaper option Mark.Hi Gray
Absolutely 100% certain. I had a Yamaha amp for donkey's years (which didn't buzz) and eventually bought a little A11 Tribute and the bloomin thing buzzed. Maybe you'd say "hummed", but you know what I mean. I think it was on this forum that I read about DC potentially causing the buzz. Rather than spend big bucks on a DC blocker, I found a guy on Youtube who reckoned a better shielded power cable might work. As it was only about 12 quid for the bits and a DC blocker is much more expensive, I gave it a try. No buzz. Put the old cable back in and it buzzed. So yeah... I am 100% certain that it doesn't buzz now and 99% certain it's down to the cable. I say 99% sure cos it's never good to be too dogmatic
It's often (correctly) pointed out on cable threads that for any cable to make a genuine difference, there must necessarily be a measurable difference.
That would certainly be the case with your cable - DC at the transformer must be being eliminated (or at least adequately reduced).
And that could be measured.
Glad your buzz got cured 👍