This article applies to: Platinum VoiceMaster Pro.
This is normal and you will find that any class A preamp does this (unless there is a relay circuit to delay the switching of the output - normally found in active speakers). The noise is caused by all of the components suddenly being charged by a DC so there is no way to prevent it other than not turning the unit on. With any recording set up, it is advisable to turn things on in the order of the signal chain - definitely, amp/monitors last. Make sure the voice master Pro is the first thing you turn on and the last thing you turn on in your set up.