bad, ill-omened, unlucky
噩 centers on ominousness and misfortune: something bad, ill-omened, or unlucky. The meanings are tightly clustered around a sense of inauspiciousness.
The exact historical development of 噩 is uncertain. It visually contains 王 surrounded by four 口 shapes, but this may not reflect the original semantic structure.
Picture four mouths (口) surrounding a king (王), all speaking bad omens and unlucky warnings. The king is trapped by ill-omened voices.
For ガク, imagine a gak! sound of a crow cawing an ill omen: gak -> ガク, and the bad luck arrives.