Only cars I own with hydraulic rollers are OEM stuff, no noise. My solid-roller car's a bit noisy, maybe almost as much as (dating myself) a solid-lifter 30/30 Duntov-cam SBC. The Street Hemi solid-flat-tappet is clearly audible, maybe a bit more than the 30/30 yardstick. My hydraulic-flat-tappet cars are pretty quiet, even with the lifter preload set at the minimum, unless they've been sitting a long time; in that case any noise isn't much and goes away quickly.