Now you’ve spent some hours playing detective and believe you have a good handle on the location and source of the noise.  For example:

The two adjacent neighbours are radiating significant broadband noise, indicative of switch-mode power supplies, as well as what may be an auto battery charger.

You have also identified some powerline noise from a power pole transformer about two blocks away.

Ensure you collect supporting evidence as you go. The best form of evidence will be written notes, photos and recordings.  Your mobile phone probably provides all these facilities.

Recording and notes are useful in the event you need to involve third parties.

Your next steps will be dependent on the nature and location of the noise.  Refer the relevant sections of this Knowledge Base for next steps.

You now need to locae the noise.  This video illustrates how to use the DF Loop.