I think the opposite is also true. I became able to sleep through nearly anything (nearly including, unfortunately, 4am fire alarms and, more fortunately, 4am wrong-numbers) in the dorms at college, where it was noisy nearly all the time.

I would imagine that exposing yourself to noise (on high volume?) 18 hours a day would cause permanent hearing damage.

18 is possibly the high end, but probably 6-8 per day, plus sleeptime, and it's never 'loud'. I've wondered about hearing loss, but I've done it for a few years now and have not noticed any loss (what did you say?) ;)