I, too, am in a career field that requires yearly passing audiograms -- I'm assuming you're in aviation. Based on that assumption, I'll throw out some things for your consideration. If my assumption is wrong, then some of my comments may not be applicable to you.

1. I've been road cycling longer than I've been in the military. My hearing has shown no loss (it's actually improved) during my time in. So based on my sample size of one (plus numerous other buddies who are roadies and still flying), road cycling isn't likely to cause you permanent hearing loss.

2. Permanent hearing loss is caused by prolonged exposure to sounds in excess of 85dB. A car passing you at 50 mph makes about 75dB, while the ambient wind noise of you riding 15 mph is around 70 dB. So the car passing you isn't going to cause permanent hearing loss, and unless you're dropping the hammer at 400 watts and maintaining in excess of 30mph for hours on end, the ambient wind noise you're experiencing isn't loud enough to cause permanent damage.

3. Even if you did experience some hearing loss from road cycling (which you won't -- and it'd be much more likely that any hearing loss you experience will be related to your occupational specialty), you're not going to instantly get kicked from the unit. You'll get a medical waiver, and get some adaptive equipment issued to you, such as a noise-canceling Bose headset.

4. Try experimenting with different head positions. I know that, for me, when I'm in the drops, I experience less ambient wind noise than when I'm on the hoods. Perhaps you could find a slightly different head position that improves things for you.

5. The noise you're experiencing could be excessive due to your helmet choice Consider going by your LBS and test-riding some different road helmets to see if that improves things for you.

6. Having an earbud in is straight up going to reduce your ability to hear cars coming up from behind you. You're blocking off one of your two input sources. Perhaps speakerphone might be a better option? You could always try it and see if you can hear cars better.

7. While riding, I'll periodically rotate my head slightly (like you're shaking your head "no") because while it puts one ear into the wind, it takes the other ear out of the wind and makes it easier to hear what's going on behind you. With electric cars becoming more common, I've increased the frequency that I'll take a look behind me . . . those Prius cars are effin stealthy, and they'll surprise the crap out of you, so I just look back more often. A picture's worth a thousand words.

I hope some of that is helpful.