Grizzly encounters are relatively rare. Of far more concern is the common Blackie that has lost its fear of humans because they are so plentiful and because we are encroaching with developments. Attacks by Blackies dwarf those by Grizzlies because of that reason. They are everywhere almost.
I've read that Grizzlies will sometimes snore like lumberjacks when they are napping. The Alaska Brownies at the local zoo don't make a sound when they move around their habitat - even on the river rock in there. Very disconcerting ability.
It's good that Blackies seem to 'talk' to themselves. You can hear them making a 'yukker-yukker' sound when they are eating tasty blackberries. I think they daydream a little because I surprised one a few years ago.
I was grazing on one side of a blackberry patch by a rail siding and I thought there were people on the other side talking quietly. I ducked through an opening to get over there and when I popped out I was within 10 ft of a medium sized black bear. I couldn't believe he didn't hear me til I was that close. He turned around and saw me and took off like a rocket - straight up a near vertical bank about thirty feet.
It happened so fast that I didn't even have time to think about the physical mechanics of retreat.
Mace for bears? Sure. Why not. A large knife? You won't even have enough time to slit your own throat if he closes with you. The fastest round-house-right by a professional boxer is pretty anemic compared to the speed and power of even a small 100lb bear.