Toa of Sonics were vulnerable to their own power, which was why there were not many of them around. Jerbraz described this as "one of the Great Beings' little jokes." The Order of Mata Nui wanted to train Krakua how to use his power to its fullest potential before he became a Toa.1
Notes
Toa of Sonics, being far more powerful than De-Matoran, did not suffer from a dangerous sensitivity to sound.2 Toa of Sonics still had acute hearing.3
Toa-level control over sonics would allow a being to shatter stone at the right pitch.4
Silence was essentially a special Sonics power.5
Power scream was sonics.6
Gray was not necessarily the primary color for Sonics just because Krakua was mainly gray.7
Someone who controlled sonics could make creatures out of sound.8