Sequencer clicks when activating Audio-track Patches

[Vincent]

Hello,
I have now about thirty stems (audio tracks, on disk) along the time line in the sequencer and now, all of them make a big click when the cursor reaches their beginnig, despite of a long fade in.
There were absolutely no click until about 20/25 stems.
I inserted silence at the beginning of them and tryied many other things in vain.
Where does it come from? Is there somethnig I miss?
How can I get rid of that?
Has it something to do with the fact they all are directly routed to the master out by 'Additional Audio Output' modules?
Why does it work great for 25, and click for 35?

Thaaanks!

[senso]

try to change the
setup/asio/diskbuffer size
setup/asio/fast disk access

and adapt it to your hardware configuration

[Vincent]

Yes, thanks Olivier, I should have specify that's actually the first thing I did! I've tryied the whole range of buffering w/wo fast disk access (and restart Usine many times) with absolutely no noticeable difference. I add that there is no fragmentation on my drives and no other disk access request.
I also tryied different levels of CPU priority (task manager), but Usine does not seem to take obvious advantage of this.
Anyway, my HD is fast, I'm sure it's not that: it works quite fine with less stems in the wkp, and it's just perfect in other sequencers with much, much more stems and no latency compensation for plugins.
It seems that it's specially when I'm running loops for mixing. Just like if the last blocks were hanging until next activation of the patch.
I'll try without 'Additional Audio Output'. Are they some kind of 'predirected' audio busses (with the same possibility of latency according to the track order)?
Even if yes, they go downward, from tracks to master out.
And, contrary to the track output mixers, they never loose internal connection with the master section, they just rock.
Well, I don't know...