I've had some hearing loss, some hereditary no doubt, some from 20 plus years of aircraft operation, some self-induced exposure to loud music and a helpful mate who let off a shotgun very close to my head when I was 18 or so - anyway, the upshot is I've got some decent losses at certain frequencies, particularly in one ear, and I get various degrees of tinnitus.
Every time I do audiometry at my medical, the doc quizzes me about it, but I've always managed to pass. The worst was a few years back when changing between defence force services, I had to do the full entry medical again, and was out of limits hearing-wise, but only on some frequencies and only on the 'bad' ear.
From there, they sent me to a specialist who did some more in-depth testing, including the speech discrimination test, and he wrote a detailed report saying that in his opinion I was OK.
So if you do your standard audiometry and fail it, all is not lost - there are other avenues you can explore to get a waiver. I know I can't hear as well as I'd like to, but I have no problems understanding aircraft radio chatter, and the specialist (if required) will be able to suss that out.
Basically, do all you can to help yourself by not going in when you've got a cold and your ears are blocked, go in the morning before you've had a lot of noise exposure, do the ear cleaning things mentioned above and you'll probably be right.
Also, someone put up an interesting link on Jet Blast (I think) the other day -
www.phys.unsw.edu.au/jw/hearing.html - where you can hear the audio tones and suss out where your problem frequencies may be - not particularly accurate due to the limitations of most computer sound systems, but an indication nonetheless.
Best of luck with it, anyhow.
"Eh .... what's that, sonny??"