Non-fan(?) grinding noise with SSD

Hi all—I'm experiencing a strange grinding noise from my Macbook Pro (2018, 15"). The reason this is strange is because 1) there's no HDD or optical disk drive 2) it doesn't seem to be the fans 3) it occurs every time I mouse over an error in VScode with the agda-mode extension, and no other time.

Here's a google drive upload of the sound. (I think it should let you play it in-browser by the preview, so you shouldn't have to download anything.) The noise occurs at around the 1-second mark, and is quite quiet in the recording; everything before is background noise.

I used iStat menus to run my fans manually, and heard no grinding during that. It seems entirely uncorrelated with fan use. I also ran apple diagnostics (by holding down D at startup), and no issues were found.

It's exactly the same noise each time, and occurs without fail upon mousing over an error.

Does anyone know what this noise could be?

Thanks!

(Note: it only occurs when the agda-mode extension to VScode is involved. Mousing over things with similar pop-up visual annotations when editing, say, Python in VScode doesn't produce the sound. Also, it happens upon running the file in VScode before mousing over the error as well—but that's the only other time. It also happens for any errors encountered in any agda files. It doesn't happen when running agda on the same file (and producing the same errors) from the command line. So I suspect it's linked to agda-mode's computation of errors in VScode somehow—but I have no idea how.)

(For the record, it's definitely hardware and not some kind of sound effect, as it occurs with my volume muted.)