For those who own or listened to these cans recently...

I recently bought these brand new from an online retailer.
My first impressions were of a very well packaged, well accessorized and solid construction pair of headphones.
Also very comfortable and excellent passive sound insulation.

I've checked the test done at headphone.com and was particularly impressed with the square-wave response at 50Hz.
The frequency response graphs show a clear tilt towards a bass-oriented response, but a good sign is there is no mid-bass hump at around 100hz. So no booming bass.

The result is a balanced sound signature - good tonal balance, and a bass that goes deep, but it's well controlled.
This is probably because these were well engineered to integrate the drivers and the on-board amplifier.

Now, what I found strange, and would like some feedback from the forum, is this: it seems the white noise/hiss coming from the headphone's amplifier/noise-cancelling circuit is a bit excessive.
Is this typical of active noise cancelling circuits?

In fact, if you put these these headphones on, and turn on its NC/amplifier, you immediately hear a fair amount of hiss - can you fell/hear the excellent passive sound insulation before you turn it on (headphone is off, no music is possible it it's not switched on) and then, when you switch it into active, the white noise comes. This is with no input, so I'd like to hear silence only or a much fainter hiss.

But if you are listening to classical or other music that has softer passages you can hear that hiss.

It this normal? What is the specification for this headphone in terms of signal to noise ratio in the on-board amplifier?