sound card monitor volume delay

Hi,

I'm experiencing something I don't really understand, and it's quite annoying.
The problem is that there is a delay between the action of turning the volume knob of the sound card and the actual sound level from speakers.

What is strange is that:
- only happens in max;
- only happens on main card output (doesn't happen in headphones output). by the way it'a focusrite saffire;
- delay time is not constant.

I get a volume ramp whose time is unpredictable... it seems to depend in some way from the "complexity" of sound, e.g. simple pulses take longer to get to the final volume (this happens in audiotester too), while a granulator patch is more responsive (but still no real-time).

To isolate the problem i tested this simple patch: what happens here is that volume has some sort of "memory", and it takes a few pulses (no matter how long i wait between each other) to get to the final volume.

Has anyone ever experienced anything like this? Any suggestion is welcome..

Thanks,
Marco