Question to Etherwave Standard/Plus Owners

Good morning everyone, I have a question for Etherwave Standard/Plus owners. After building my Etherwave and enjoying it for a couple of years, I would like to try improving the volume control. More precisely, just before complete silence, about a couple of centimeters from the volume antenna, there is a strange sound like "vrrrm." It is not noticeable during quick execution, but when fading slowly, it is. Does this happen to you?
I have another question for the experts here on ThereminWorld: where can I make the correct modifications to fix the problem? Might it be necessary to change the value of a resistor like R37 or a capacitor in the U3-B area?
Thanks in advance.

Attached is an audio file recorded with a smartphone.

https://drive.google.com/file/d/1gZmF0lrLTgogtXZ33u54Yf-oy1NFxIV4/view?usp=sharing

Still with these writings...

I couldn't hear an obvious "vrrrm", so it would be nice to have a video to see when your hand is getting close to the volume antenna.

One thing I'll mention is that your volume hand can change the pitch quite a bit when it gets close to the theremin.  Usually this is masked by the volume dropping, but depending on how your volume field is adjusted, it can become obvious.

Hi Edavid, thanks for your response. So, essentially, you're suggesting that if the volume setting is too high, one might perceive this strange sound? Unfortunately, I can't check with another theremin since no one in my area even knows what it is... a shame! Anyway, I think it might be possible to better attenuate or filter the last sound before silence. Before picking up the soldering iron, I'd appreciate the opinion of someone who can guide me on where to intervene. This strange sound is more noticeable with the amplifier volume a bit high while being close to the limit with the hand on the volume antenna.

Hi Edavid, thanks for your response. So, essentially, you're suggesting that if the volume setting is too high, one might perceive this strange sound?

I am not saying that, because I didn't hear anything strange in your audio file.  I am just guessing about what the problem might be.

It would be good if you made a video showing your hands.

Also, a simple thing to try would be to keep your volume hand farther from the pitch antenna when you play, and see if it makes a difference.

First of all, there is a constant backround humming sound (probably 60 Hz from the supply).
Then I clearly hear the vrrrr sound at low volume, especially at 0:39 an 0:56.
It's like a modulation of the theremin's sound by the humming sound.
Diificult to understand the cause of that problem from a distance !

Thanks for the advice, Edavid and André. As for the background buzzing, it's directly caused by recording near the smartphone amplifier. I'll conduct further recording tests, perhaps even with video. Thank you.

Is your theremin homemaded?

If so check the C27.

In diagnistoc purpose yuo can try replacing it by 1...10 uF.

Thank you, ILIA, for this insight you're giving me. I'll try to change the values of C27 as soon as possible and I'll let you know. Yes, I built my theremin myself using the electrical diagram I found on ThereminWorld.
I made a new recording using the NUX pedal. Now the issue should be more noticeable when listened to with headphones
https://drive.google.com/file/d/1CIV1_JdxYbvaaj7p7RflRnZFK6SNSM1e/view?usp=drivesdk

https://drive.google.com/file/d/1CIV1_JdxYbvaaj7p7RflRnZFK6SNSM1e/view?usp=sharing
This is the right link