There are good hyd cams that are quiet,but I've seen (or heard!) a lot of hyd cams that make a lot of noise and often have issues before they get to 6000 rpm's without spending more $$$ and time than any hyd cam should receive. Why anyone would grind them is anyone's guess,but my is the cam grinders have realized the public will buy what looks good(aggressive on paper) whether it works in an engine or not. There is MUCH more to a cam than what can be seen in the lobe charts and the few reference points given by the maker(often not accurate either). Most of the noise complaints are caused by the closing ramp(or lack of),but that doesn't show up in the lobe specs.