Here was my situation yesterday morning.

All went as well as I could ever have hoped.
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My "gig" is Church, and that's what I bought this bass with the intent for. Basically run the GK MB115 as a "pre" as well as a monitor for the sound system, currently. However, something very interesting happened to me yesterday.
I get to our rehearsal room, plug in, and no hum at all. This bass is dead silent, as it should be. ("He says, as he scratches his head, baffled.") We use a Rumble 25 in the rehearsal room. When I plugged into the GK, same thing.
Rumble 25 and GK MB115 are my identical home set-up, albeit I have the updated GK. (?!?) Seems like this bass doesn't have a pre-amp issue. I must have some sort of interference issue at home, which I already knew. My printer can make my home set-up buzz too. What remains weird though is that my Satin M5-24 doesn't buzz at home. Also weird: sometimes the hum on this new one isn't bad at all which made me wonder if I was going crazy imagining things. So...I have no idea. But it all sounded killer yesterday!