Generally for an existing system the cable doesn't change except for:
Construction or repair — Any workmen in the building recently?
Any new equipment or cabling of any kind? (Telephone, Data, Electrical . . .)
Was UTP used as speaker wire? If it's used on talk-back speakers may lead to higher electrical noise.
Be sure to check for proper AC grounding using a 3 Wire Receptacle Tester. It's not, hopefully, your responsibility to correct AC wiring but verifying your receptacle is properly wired and eliminate hours of searching for ghosts.
...and of course all the things Hal stated.
