Disk Utility reports "missing thread record" on my external HDD
That sound you hear is often referred to as "The Click of Death": https://en.wikipedia.org/wiki/Click_of_death

Head reader errors, motor errors, anything of this sort indicate physical failure, and possibly imminent device death. Get your data backed up off of that disk NOW.

Afterwards, and only afterwards, check and see if it's still in warranty. :)