My understanding is that the Sound is coming back right now.
In 4.5, you had
Matoya's magics shorting out. A few people I've talked to have attributed that to the Light aether from the First, but light aspected aether shorting out magic is not an effect demonstrated in the story. What is? The Sound. at the end of 5.0 we learned that the Sound warped the magics the Ancients used.
Then, in 5.2,
Urianger heard a sound which ruined his water walking spell. In 5.3,
Alisae and
Y'shtola hear the Sound as well. These incidents are distinct from Thancred becoming tired due to his soul being divorced from his body.