reaper to the grave for me
splitting hairs here: many listed here are not editing programs like in the original question. keep in mind you sometimes need an editor that will actually manipulate (= destructive editing) the source file. as in chopping a piece out of it or correcting dc offset. for these kinda works you will need wavosaur, audacity, sound forge, peak, etc...
old classic: check out what happens if you take some file and change the extension to wav... here you also might need to reopen it in an editor instead of foobar/itunes etc
edit: everyone should buy a reaper licence. its a stinky 50usd to support the most flexible ninja tool for digital audio ever. it does all +more of the stuff that programs with a tenfold pricetag do.. and its portable, you can run it floating, no need to install solidly!! i been to protools studios and popped in my usb stikk to work with them hd rigs, you should have seen the faces of the studio owners
also: theres a free older version of audition floating round the www which is a good editor and has xlent restoration tools (hiss + crackle filters... its the opposite of whats needed in noise haha, but still, sometimes you need to clean up vinyl rips or cassette transfers)