I found where it is. It seems to appear on my desktop box when I connect cams to the same bus. Two connectors next to each other. But on the notebook it does matter. Any bus, any port. Problem still alive with a kernel 3.0.2-pf-di #1 SMP PREEMPT Fri Aug 19 00:21:22 EEST 2011 x86_64 Intel(R) Core(TM)2 Duo CPU E8200 @ 2.66GHz GenuineIntel GNU/Linux //D