I doubt the handbrake drum was causing it, but it's easy enough to leave the adjuster slack and go for a test run. If it continues then you look elsewhere. Since I haven't heard the humming, it's not a diff-like sound is it? do you get a clunking from low speed changes of direction too? eg when parking? Maybe leave the rear prop off for a test drive and see what happens to the sound (obv you can't leave both props off at the same time lol)
I find acetone on the brake pads helps get the leaked oil off efficiently btw
I find acetone on the brake pads helps get the leaked oil off efficiently btw