Serious problems during export/mixdown

I encountered a serious problem when mixdown my project.
I got a permanent noise during all the playback. Obviously the noise is not present in the original mix, it’s only generated when the project is exported.
Bouncing all single tracks & groups I noticed that the noise is created inside a group channel track which contains guitars with vst amp rack by steinberg in insert. Even if I mute this group track the same noise is created during export.
This is the first time I encounter such a problem. I’m a Cubase user since beginning of 2000.

Anyone could help?
thx in advance

Check the channels strips in the mixconsole. I had a similar problem back awhile, and it was because I had used a Cubase template which had placed some effect in the strip which was causing the problem.