Impreza Outback Sport winter braking???

I hope someone can help me, a few months back We bought a 01 Impreza Outback Sport . It is an automatic with 80,000 miles. I love the car, but noticed now that its snowing that when you get on the brakes, on slick roads you can feel the brakes, almost grabbing hard. They seem to pulse, and you sometimes hear a buzzing sound. My other Subies were all 80's models, and manual trans. and selectable 2 or 4wd. so this one is very new to me. I dont know if it could be something with the auto trans and the "wheels that slip" traction control, or maybe it is from the anti lock brakes ( if so equiped)and the all wheel drive system? I have noticed that on very slick snow covered roads when braking you can feel the brake pedal going further down, not alot, or right to the floor, but its a noticable movement.
Sorry for the long post, but its hard to explain. I hope someone knows about it, Thanks in advance for any help.

Bill.

It's the abs system working to prevent your wheels locking up in slick conditions.

I was kinda thinking (and hoping) it would be something like that ,instead of an expensive repair. Its a really really strange and uncomfortable feeling to get used to though thats for sure. what would cause the buzzing sound though, only heard that twice so far, but strange non the less .

My 97 OBS does this also and i hate it. Last winter i had new but not good for snow all season Cooper tires and it wasn't too bad but now with 20k on the tires it's back to doing the uncontrollable skids. I feel that 4 SNOW tires will help and hopefully prevent this dangerous trait of ABS. I'll find this out next year when these tires wear out.