I have played tuned percussion in a 30 piece brass band for 16 years. This consists of 2hr rehearsals, twice a week. I would imagine that of that 2hrs, <1hr is spent in a "loud" (100dB) environment.
Theres your answer. I'm very suprised that you're suprised with the results as this type of activity is very damaging to your hearing, I have moulded ear plugs for when I play in a band or do sound engineering.
Here is a site with more information on hearing loss and damaging sound levels:
http://www.dangerousdecibels.org/hearingloss.cfm