Hey folks. I've been away a while, though I generally read way more than I post anyhow. I'm back to ask your assistance with a bad hum issue. I just finished building a speaker extension cabinet from scratch, first time trying it, happy enough with the end result. However, to the issue: I mounted a brand new Cannabis Rex. I'm trying to run it from the "Speaker Output" jack on the back of a Fender Bassbreaker 007 combo listed at 7 watts, 8 ohm min. With extension cab plugged in, everything seems fine for the first 10 to 20 seconds after turning on the amp. Then a loud, obnoxious hum swells up. My phone app says the hum is at 65.8 Hz. The hum is not present through the stock speaker when the extension cab is unplugged. So far I have tried a ground lift plug on the wall, two different cables between amp and cabinet, swapping the + and - leads from the jack to the speaker itself. Volume and gain controls have no effect on volume or pitch of the hum. I'm planning to take it to church tomorrow where I have my Princeton Reverb RI stashed and try it with that. Music makes sense to me, electronics do not, but I'm trying to learn. Help me out folks, what do I need to learn here?