Thumps or pops delivered from an amp to any type of speaker driver thumps or pops is not a good thing and should be avoided. This is true even when talking about the most expensive sound drivers in $8000.00 wedges. The system operator needs to be careful to sequence power and signal devices such that pops do not occur. Pops are really a voltage transient that occur when there is energy stored in a circuit component. So for a large PA system, we recommend turning the signal devices on first and let any transients bleed out and reach a steady state before we turn on the power amps (true for an iPod as well). We reverse the order when shutting down.
Another issue that can arise is if the power amp (the headphone amp) is not happy driving low impedance IEMs. To avoid problems of this nature, we suggest buying an inline volume control for less than $10 available at retail electronics stores. Turn the volume (it’s just a variable resistance) all the way down and then turn the system on. The in-rush current will be resisted and much of the voltage will drop across the resistor. Thus, the armatures will experience a much smaller (if any at all) pop or thump.