If you place a block in the air when it's raining then you move around the sound of the rain will glitch in a weird way.
(In the video you can see an other bug, that I already reported.)
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I've tested it in 1.15.2 and found out, that the weird sound is the game rapidly changing the sound in the left and right ear. I think it's between the normal sound, where the sound is louder in the side closer to the block, and being equally loud in both ears. Turning the camera or moving changes them rapidly. It happens at the coordinates near 300 000 000 ~ 0, but not at 0 ~ 0. At reproducing the problem placing a repeating command block with the command playsound minecraft:weather.rain master @p ~ ~ ~ 100 while it's always active, then moving around it while looking at the block might help. Also, it can be a problem with my computer or my sound software if you can't reproduce it. I use the program Realtek Audio (Console) by Gigabyte at the version 6.0.8703.1 with the user interface version of 1.3.180.0, so that might be the cause of the problem. If this is a personal problem I can live with it, no need to help. I hope this will help solving the issue.
Seems probably caused by MC-177725
Cannot reproduce. Please check if that's still an issue for you in the latest release. Also please provide more details about this issue.