Rather than a "whistling" noise I've heard quite a few R44s exhibiting a "squeaky wheel" noise. The only other helicopter I've heard do that was a particular Mil-8 towing a full bucket of water which was very disconcerting, thankfully it went U/S and the swash plate problem was attended to. I'd like to think this isn't the same kind of problem in the R44, which it is considerably lighter and maybe just a design feature.