Windows movie maker is indeed one of the most popular and FREE video editing tool available with most of the windows versions.

If you also use it to make your videos and have been struggling to remove the background noises like the hmmm, hiss sounds that have got into your video even when you took all the precautions while recording, you can use Audacity (FREE audio editor) to remove the noise.

Here is how you can do it.

1. Download Audacity and install.
   
   
2. Import windows media file (generally in .WMV format) in Audacity. If this is the first time you are using Audacity, it will throw an error that it could not identify the type of file.
   
   Solution:
   You need to download an add-on codec which can help Audacity help read the WMV files. Go to- Edit->Preferences->Libraries.
   choose ffMpeg and click 'Download' button. Once downloaded and installed, the ffmpeg section would show the version information as follows:
   
   
   
   
3. Now, close Audacity and re-open.
   
   
4. Go to File->Import->Audio
   Select the .WMV file and click OK. Audacity will automatically import the Audio from the video file that you have selected.
   
   
5. Now, you would see the audio layers like this:
   
   
   
   
6. The removal of background or any other noise (unwanted audio) is a 2 (two) step process.
   1. Select the Noise Profile: It is nothing but a sample of audio that you consider as noise. Audacity will record the noise and will remove it from the selected portion. Even a one second audio is good enough to create a noise profile sample.
      
      
      
      To create a Noise Profile:
      Select the portion and then click Effects->Noise Removal.
      
      Note:If you find the menu option of Noise Removal disabled, make sure that your audio is in 'STOP' mode. Sometimes, we are listening to audio and press ' Pause' button and then select the noise portion. Audacity wants you to completely STOP it before taking any action.
      
      A small pop-up will come up. Click the button 'Get Noise Profile'. It will record the noise profile and remember it in memory.
      
      
   2. Remove the Noise from Audio: Just select the portion of Audio (press ctrl+A to select full audio) that you think contains the noise.
      
      Click on Effect->Noise Removal again. Select the second option 'Remove' now and click 'Ok' button. This will remove the noise from the selected portion. Listen to the modified audio and the noise should have gone now. Save the project to avoid any loss of work.
      
      
      
      
   
   
   
7. Save or export the modified audio file as .WAV file by using File->Export. You can save it in any audio format you like.
   
   
8. You can now use this sound file in your windows movie maker project easily.
   
   

I hope this helps you in removing the unwanted noise or background hiss. Enjoy!