To enable the performance of Expert D inside a compact flash, so-called switch-mode power supplies have to be used. Otherwise, the units would become too large and heavy.

Switch-mode power supplies work with high switch frequencies. This may cause noise development which is completely normal and ok. Even small switch-mode power supplies as used in computers or televisions are rarely completely silent. Even more powerful power supply units are used in professional flash units than in computers or consumer electronics. More powerful switch-mode power supplies are, however, more noise intensive.

People who are used to working with conventional units may think that the humming and cracking noises of flash units in use are unusual. But this is completely normal for such units and absolutely no technical problem. The noise intensity also depends on the quality of the power supply and the operating temperature.