The texture was intentionally made to look like that, so it's not a bug. If you dislike it you can suggest for it to be changed here: https://feedback.minecraft.net/hc/en-us
I attached a video showing it. I have player sounds turned off on the Blue__Guy account and player sounds turned on on the account I'm recording with. You can see that the sound only plays for when other players swap offhand items. (don't mind the watermark I had to decompress the video since it was too big of a size)
Ben 
MC-234535
The texture was intentionally made to look like that, so it's not a bug. If you dislike it you can suggest for it to be changed here: https://feedback.minecraft.net/hc/en-us
Oh, I didn't realize that. I thought it was a bug since the texture had been different in previous snapshots.
I attached a video showing it. I have player sounds turned off on the Blue__Guy account and player sounds turned on on the account I'm recording with. You can see that the sound only plays for when other players swap offhand items. (don't mind the watermark I had to decompress the video since it was too big of a size)
I just tested it on a LAN world and I can't hear it at all. You might be right about it being a spigot thing or something like that.