In stereo bypass mode with the mains set to "large" you should get no signal at all to the sub. In stereo bypass mode with the mains set to "small" you will likely get a little -- in that scenario, the 950 sends the unaltered analog signal to the mains, but also passes a copy of the signal through A/D conversion and bass management to produce a sub signal based on the crossover point set for the mains. I've got a detailed overview of the 950's bass management here that you might find useful.

Outlaw's very good about repairs when it is necessary. As bossobass suggests, you may be running into a ground loop hum of some sort on the second item -- at least so far, it doesn't sound like a defect in the 950 itself.

------------------
gonk -- Saloon Links | Pre/Pro Comparison Chart | 950 Review