Octopuses can't hear (except for tapping on the glass, or deep vibrations), so the vacuum cleaner or yelling won't bother them.
They tend to ink when startled, when they're "spooked" by something they didn't expect. An example - my bimac last year, Ollie, was asleep on the glass when I came to her tank first thing in the morning. I thought she was awake, so I turned on her light. She "jumped", inked, and went zooming off. I believe she inked 4 times in the 10 months I had her.
Nancy covered it but just to reinforce the that the main cause of inking is sudden movements or bangs... like a door slamming, but as said, switching the lights on is always a bad one, its better to let another small light come on for a while somewhere else in the room
I have only had my guy ink once maybe twice in his tank the whole time I have had him, and I just startled him he turned orange and shot off to the back behind the rocks, then peeked out, saw it was me and came back out. The ink dispersed almost immediately, its not a lot at all, and luckily he shot it right into the filter intake, not that the filter does much, but the protein skimmer will handle it no problem.