GWC last I checked hadn't been developed in some time.  Hadn't heard of auphonic, will have to take a look right now.

Others have given good comments as chances are for traffic noise which can be variable can be difficult to filter out of a recording.  Note that I didn't say remove, or even denoise, as neither of those are accurate and you will never end up with an identical quality recording as if it wasn't there, or really even close in many cases.

Personally at the moment I am using Festige combined with WaveARTs MR Noise for realtime noise reduction on Linux.  This was extensively used on the recent video that was part of the Tube Kickstarter campaign (ABout 16 instances of thise IIRC combined with other tools that were suggested elsewhere in this thread).  But Ricardus is completely correct, I have yet to find quality noise reduction tools on Linux.  I do need to check out the aforementioned auphonic however, hadn't heard that.

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