[Chas]

That is the sound of an inverter, generally a Solar Panel. However, SCR devices can make that type of broadband signal to.

Does this sound come in on other AM radios in the same location?

Do you have a battery operated transistor portable radio, a larger size preferred?

Does the sound come in on that radio too?

Many other modern household appliances with computer like function panels can generate that form of noise.

With the portable radio one can hunt for the sound, the long ferrite antenna is directive so turning the radio and walking at right angle of the radio at its loudest will direct one to the noise source.

Go to this link at the ARRL:

http://www.arrl.org/radio-frequency-interference-rfi

There you will find other links telling you how to find the noise problem and how to fix problems is the home.

Over the past few years, I have been plagued with RFI on 40 and 80 Meters.  Most of it has been Horticultural lighting, (read that as Grow Lights). The power supplies for the LED's in these lights are the high power switching type. Similar to that in a computer...

I am a Ham and experience noise issues all the time.

The linked remark about lightning arrestors can often be identified as a "tail" hanging out of the porcelain body of the arrestor. The inside is smoked with blown apart metal and it is arcing inside.

A bad arrestor, insulator, transformer can create a noise that travel for miles on the high lines... Clamps to the connections of the arrestor can generate noise if they are loose...

Chas

WA1JFD