My mouse occasionally goes unresponsive for a few seconds (keys still work properly, so it's not a general game freeze), then resumes with Windows playing its standard "something just happened" sound, with no clue whatsoever what happened.
This has started only recently, though I can't tell for sure what change got it started; some gut feeling tells me it might be related to the LWJGL version bump. (It might even be something entirely unrelated to Minecraft, but so far I haven't encountered the glitch anywhere outside the game.)
Any ideas how to narrow down the root cause would be appreciated.
Check your mouse, maybe your mouse cable is broken. The sound you'll get may be the "Plugged in a new device" sound.
Plug your mouse in a different USB port
Use a different mouse