My current bag is old and far too large. I also have thigh rub with it and want to eliminate that.

Do those of you using the bags with clip/straps on just the rails, does the bag bounce around make noise all the time while riding?

I'm trying to get a bag without the seatpost strap to avoid shorts rub and since my current bag strap is scratching up my nicely finished seatpost. I'm just wondering if the rail-only secured bags rattle constantly.