Nagra VPA and Meridian 601 preamp.

I am driving a Sonus Faber Stradivari Homage with Nagra VPA and Meridian 601 preamplifier using the balanced output.
when i power on the VPA and switch from mute to on (after 2-3 minutes) i hear a small 'bang' , then everything sound good.
what could be this problem?
Mine also do this. Try leaving on for a longer amount of time. It could also be normal. Nagra has an office here in the states. they are good at answering questions.
It is normal ,,, the relay in the VPA , it is used to prevent sudden voltage damaged the speaker unit... All the extreme amp have this features...
It is not normal ! I have never experienced this with my VPA's. I would check with Nagra Service.