Low frequencies are a dull rumble, high frequencies a shrill whine. As we get older, frequency response drops. The human ear is most sensitive to sounds in the 1 to 4 kHz range, the usual frequencies of human speech, and damage occurs first in these areas. Hearing loss is a gradual process unnoticed by the loser. Above 105 dB, your hearing can be damaged by repeated 15-minute journeys.
Motorcyclists risk hearing loss.
Noise is the constant companion of a motorcyclist, no matter how quiet the bike. Pushing any projectile through the air at speed creates turbulence and noise, whether that projectile is a rifle bullet, an airplane or a human head. Riding with a bucket on your head creates more turbulence at the mouth of the bucket, and more noise. Even the best helmets can't close out all the wind noise, so if you ride long distances frequently, you need to wear ear protection. Unfortunately, they are all breaking the law.