Following last days post on cleaning up your recordings I’ll give you a list of a couple of helpful plug-ins and applications that are specialized on this task. Most of these are rather expensive, but they can prove to be worth the price.
Waves is a classic plug-in developer in the audio department and has since the dawn of times been considered among the best. Lately however they have taken a few odd turns, including a strange support system (WUP) and a witch hunt on pirates. This has lead to them having a rather bad reputation as a company. Anyway, the Restoration Bundle contains X-Hum, X-Click, X-Noise and X-Crackle. Pretty self-explanatory.
Also a giant in the pro audio field, Sony Oxford recently broke with Sony and became Sonnox. Their other plug-ins seem to still be for sale, but not the Restoration tools. it is possible that Sony kept them to themselves.
See a pattern in the names of these products? Wave Arts (not to be confused with Waves) have gotten some good reviews and are cheaper than much of the competition.
While all the products mentioned above are plug-ins to use in your audio editor, BIAS Sound Soap and Sound Soap Pro are full applications.
The ones I’ve mentioned here are commonly used among professionals, but remember that the price tag doesn’t measure quality. You’ll very likely be able to find cheaper products out there that might work for you. You’ll probably even be able to find free or never expiring shareware for audio restoration tasks.