First off, you're best off asking these kinds of questions in Bicycle Mechanics forum.

You have an aluminum alloy freehub? What kind of hub is this? Aluminum freehubs are a bad idea with most cassettes. For a short while Shimano used an aluminum freehub for their upper-end 10-speed stuff, but the splines were taller to prevent the cogs from digging in as much. These were only compatible with 10-speed cassettes because they contained corresponding deeper grooves. I would guess that a cassette with a carrier would minimize the larger cogs from digging in, but the PG970 doesn't have a carrier, it's just a collection of loose cogs like the PG950. (Edit: I can't tell from pics online whether the PG970 has a carrier.)

Which cassette did you have on it before?