The only ones I can actually hear are the bigger props some of the sport guys use at our club. Even then only really while the prop is slowing the plane down in a dive. The clearest prop sound I have heard so far was this one http://www3.towerhobbies.com/cgi-bin...?&I=LXGAE5&P=7 and it was on a giant Big STIK. It was really noisy in a dive.