Fred Cohen sums it up perfectly in this excerpt; " Helicopters rank especially high in causing undesirable noise. Eight different studies have found that the annoyance created by a helicopter does not correlate with the decibels it registers. The helicopter’s unique sound, created by blade vortex interaction, causes people to rate its sound level as much as 10 dB’s higher than it actually registers, doubling the noise impact. This would place perceived helicopter noise at around 97 dB, or a whopping 30 dB’s over the generally accepted noise level of residential areas. These findings certainly suggest that helicopter flight should be regulated in response to the exceptional levels of noise they produce.  Despite the findings on helicopter noise and the aesthetic-health issues linked to excessive, annoying noise, local and municipal legislators have no jurisdiction in this field of noise regulation — leaving us to bemoan our fate, visit a BOSE outlet for noise cancelling head