I am a university music major, and just took a class last semester "Occupational Health in Music," whose professor was in the middle of doing a hearing loss study. I learned a LOT about hearing loss from that class.

First off, there are different kinds of ear plugs that effect your hearing differently. Many (like the foam ones) disproportionally filter out frequency levels - some things are harder to hear than others, but overall db level is reduced. I acquired some musician's earplugs that pretty evenly reduce all sound by 20-25 db.

Secondly, the amount of damage caused by noise varies a lot according to db level and TIME of exposure. Generally, anything above 80 db is considered "dangerous," since you only need a small amount of exposure time ( about 15 minutes, if I recall) to begin hearing damage. If you listened to 40 db for hours on end, this would probably cause hearing damage. The higher you go past 80 db, the exposure-time-until-damage gets increasingly smaller and smaller.

I highly doubt that riding with 20-25mph wind causes such high db levels. If this were so, if you rode for an hour or more, you would probably get temporary tinnitus. Also as already mentioned, head position and traffic patterns effect this. I doubt any sort of db level, be it high or low, is consistent.

Oh, tinnitus? That's the sound of your ear cells dying. They're these little hair-type things. Also, that pitch your tinnitus is ringing at? You'll never hear that exact pitch again.

This class has made me very aware of db levels and the risk of damage even in places you wouldn't normally associate with high db. For example, waitresses are at risk since they are in fairly noisy environments for hours at a time, every day.

I wouldn't completely rule out the possibility of hearing loss from wind in your ears, but when I ride things are pretty silent. I can even hear the slight whipping of my tires on the ground, when no cars are nearby.