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From: piglet <erichpwagner@hotmail.com>
Newsgroups: sci.electronics.design
Subject: Re: signal leads that pick up less ambient noise?
Date: Fri, 21 Feb 2025 13:23:33 -0000 (UTC)
Organization: A noiseless patient Spider
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Christopher Howard <christopher@librehacker.com> wrote:
>> Frequency??
> 
> I'm not sure exactly, but when I zoom in to it on the scope, the noise
> appeared to have a regular ebb and flow of about 40 Khz.
> 

That seems very likely to be from some power supply, either wall wart or
built into some equipment.

A great EMI sniffer to sleuth out is an old school $5 pocket AM broadcast
radio (the kind slightly larger than a cigarette pack and powered by 2 AA
or 9v block battery).

-- 
piglet