Room noise is one of the many frustrations that come with home recording. Computers, neighbors, and even just less-than-great acoustics in the room you’re recording in can all show up on your raw track. There are pre-made attachments for your mic that can filter out some of the higher end noise, but why not save your money for something else? These foam DIY reflection filters don’t make a huge difference, but for the low cost of materials, the subtle improvement is worthwhile.
For information about how to build a DIY reflection filter, and some before and after audio examples, read here: http://www.prosoundweb.com/article/in_the_studio_developing_a_homemade_reflection_filter_with_audio_examples/