Many many many years ago, when I was a welder, the company I worked for, took an entire afternoon and shut down production, and had a hearing specialist come in and give a speech about hearing safety. No one cared, until she grabbed one of our co-workers and performed a 30 second hearing test. Then she proceeded to tell him:
You drive with the windows down, and you ride motorcycles frequently with around 200-400cc motors. He said "that's impressive, how did you know that?". She referred back to her hearing loss chart, and said "well you already show signs of hearing loss in this range which is from wind noise, and since it is only in your left ear, this means only your left ear is exposed, such as driving with your windows down, sitting on the left side of the car, and you show signs of hearing loss in this range, which is typically from motorcycle engines in the 200-400cc range. The next guy she pulled from the crowd, she could tell he was into shooting guns, he shot right handed, and what calibers he favored. I started wearing ear plugs after that. I also wore them racing motorcycles, as well.
a Few years later I got into Jet ski's, and didn't see the need for ear plugs. Then My first season riding I had two sinus/ear infections, and my doctor explained that when I would hit the water, and water went up my nose, the pressure relief system in the ears let the air of the sinus cavity out, so water under pressure would go up in the sinus cavity, and cause infection (the lake I was riding in at the time was pretty green). So after the second infection in two months, she insisted if I would wear earplugs for the rest of the season, I would have no more problems (b/c then then the entire sinus cavity would be under pressure and if air could not get out, water could not get in). Needless to say, I have never ridden without ear plugs since, nor have I had any sinus/ear issues since.
The best deal on ear plugs is at Home depot:
http://www.homedepot.com/p/3M-Tekk-Protection-Reusable-Corded-Earplugs-3-Pack-90716-80025T/202195388