Hard drives are mechanical devices, they have moving parts.You have platters, where the information is stored on, that almost constantly spin around while the computer is on, especially when the drive is in use. There are also read/write heads. They are just above each platter and the swing back and forth when read/writing. Think of a record player and you'll get the idea.
Your problem (getting louder and louder) sounds like, to me atleast, the drive was wearing down. The bearings the the platters spin on might have worn out. Less likely but ,it could also have been a problem with the heads. When they wear out, sometimes the heads smash onto the platters, destroying the drive.
Replacement is the only option.