Another way to reduce noise using Audacity

I think this works - tell me how it works for you:

If  you have bothersome low-level background noise in your audio, try this:  Choose Amplify from the pulldown menu, and amplify by about -15 dB.  Choose Leveller from the pulldown menu, and set it to Light and to Noise Threshold of -20 dB.  Click OK.  After the processing finishes, choose Amplify again and click OK to raise the level by the suggested amount.  The softer noises that were deleted during the Leveller processing don't come back up.