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On my QMX (mid-band), I can hear a constant tone on some frequencies, as if someone is tuning up an antenna, but it just stays. It also doesn't make a difference if I have an antenna attached or not, so it's not an actual signal, but seems to be internal to the QMX. In a way it behaves as if it's an actual received signal, in that it shows on the S-meter. For example, on 14,074,80 I have a pretty loud one, showing 4 bars. But in another way it's not like a received signal, because when I tune slightly away from it, the tone disappears instead of changing in pitch. For example, the "signal" on 14,074,80 is completely absent on 14,074,79 and 14,074,81. I'm powering it from a battery, so it's not power supply noise.

Also, I can change the frequency of where I hear the tone by changing the CW offset. For example, when changing the CW offset from 700 to 800, the tone mentioned above moves to 14,074,90.

The tone I hear has a pitch of 820 Hz (measured with an app on my phone).

Has anyone experienced this, or know what could be causing it?

Hello Willem,

What you are hearing are internal "birdies" generated by the SMPS. It is a known issue, and it's on Hans list.
There was a discussion some time ago, please see this post.

Regards,
YO3GFH
op. Adrian

Hi Adrian,

That is great news. It's good to know there's nothing wrong with my build. The birdies (new word to me) don't really bother me, other than a slight worry that maybe there was a defect in my QMX.

Thans!
VA2WLM -- Willem