Go and get an audiometric test. It’s not at all unusual for hearing loss to occur by your 30s. If you are worried it’s a good way of marking where you are and taking steps to minimise any future damage. Quite often your company may have an occupational health provider that can do it. Costs around £45.
And no, unless it’s a temporary threshold shift caused by listening to loud music on your ipod or your missus nagging you tonight, it’s not reversable.
Might also be caused by a build up of wax in your ears too. Are you a dirty bastard?