CommentStreams:F6832af244d460d84bd8f9190bc549c8

It comes from the bottom right corner, where type-c and Raspberry power pins are (#1 in the picture above). It's hard to say more precisely.

- The board version is 1.3 - Sound exists both with and without a heatsink - I also noticed that the sound may disappear if I press down the heatsink with great power. But unfortunately screwing it hard didn't help.