I received some emails from a previous post in the Antenna Forum, so I decided to repost again and have added some pictorials of a typical switch-mode power supply RFI signatures per those requests. Below is a recap of my previous post - it is better suited in this forum.
1. Most of the time, in a rural setting, power line arc-faults are the predominant RFI offender (power utilities often recognize the term 'gap noise' instead of arc-fault). In urban environments, it is not uncommon to have simultaneous RFI emission sources and you will need to methodically sort out each source independently.
2. Although better than nothing, the use of a hand held AM radio has some notorious limitations: (a) RFI at broadcast frequencies can travel quite a distance. Power distribution lines make good transmission lines at those frequencies. (b) using your ear to determine both the amplitude and noise signature of the interfering source is poor, at best. A hand-held AM receiver is better than nothing but be cautious that it could mislead you.
3. Do the obvious RFI housecleaning at your location, first.
4. Most RFI has distinct emission signatures - see examples below.
5. Over numerous years of helping others track down offending RFI sources, I have graduated away from many of the previously utilized snooping methods (spectrum analyzers, VHF/UHF/ultrasonic sniffers, etc) to just a few items - I have found that just a few specific pieces of equipment will effectively identify the offending sources about ninety percent of the time. That equipment includes: a receiver (see below), variable attenuator, small loop antenna. The remaining ten percent of the RFI required some of the other equipment. The point is that you will probably be able to track down most RFI sources without special equipment.
6. Many RFI signatures have a distinct 'time-domain' signature and modern day receivers/transceivers, such as the widely used IC-7300, includes an audio scope capability. That capability provides an efficient pictorial of the RFI signature, most of the time. Follows are a few examples of those signatures that I captured using my mobile IC-7300. You should be able to capture similar signatures at your home QTH as a starting point.
To correctly snapshot the RFI signal, you will want to go to the AM mode, noise blanker off, wide pass-band, audio scope time set to 3mS/Div and the frequency(ies) of interest.
Here is a picture of the most common power line interference signature in a typical QTH environment (single phase 12+ KV distribution). It is a typical example of an arc-fault. This is an image from my SUV's IC-7300. The most important attribute is the inter-pulse time - it should measure 8.3 mS (since the IC-7300 cannot sync to waveforms, you'll need to press the hold button to stop the sweep)
The 8.3 mS is determined as: 1 / (60hz x 2) = 8.3 mS (remember that one sinusoidal cycle has two peaks so you'll see two noise spikes per cycle)
As you can see, attempting to assess the RFI signature using the frequency domain on the left isn't very useful.

The following is a capture of arc-faults on a 3-phase distribution line. The key attribute is, again, the ~8mS inter-pulse streaming time - that give-away points to arc-faults. Most likely, the source are power lines if it can be detected at a far distance from the source. But an arc-fault at a residence can result in a similar signatures but will, most likely, be weak at a distance.

Here is an example of a arc-fault inside a bad distribution line compensation capacitor. The location of this capture was ~1/4 mile away from the eventually identified root source using 90 dB of attenuation - quite noisy, indeed. The RFI signature changed with temperature. The waveform is similar to the above three-phase thumbprint but with a subtle difference.

Here's a frequency spectrum view of a typical switch-mode power supply (SMPS). Note that the spacing of the harmonic emissions are about 75 KHz (+/-) (notice the noise bursts at -30 & +40 KHz in the picture). This is a picture of a nearby SMPS interference that occasionally pops-up at my QTH - the picture is from a TS-890S but would be the same on similarly equipped radios.

Here is a close-up of one of the harmonic emissions. Note that it is a spread spectrum emission. This is due to the commonly used SMPS frequency dithering. There are also fixed frequency SMPS's, but the dithering mode is more prevalent in supplies that will, more likely, cause you problems.

Here is a view of the frequency and time domains of the SMPS. Notice the distinctly spaced RF emissions on the left spectrum view. It shows the frequency hopping. As a contrast to arc-faults, the time domain view on the right provides less useful information.

The main reason for posting this information is that, many times, one will look at a frequency spectral display and can not decipher the information. But, also assessing the time domain information of the RFI, as well, may be the key to unlocking what the prime suspect is.
Feel free to drop an email to me if I can help you interpret RFI signatures that are impacting you .