[LAU] USB on ThinkPad T520

greetings! i've been running AVLinux5.0.3 on a ThinkPad T61p for a while now.... with an ART USB Dual Tube Pre, i can run Jack at 64 frames, 2 periods (2.9msec latency), and run a puredata test patch of mine with almost no xruns -- maybe 1 per hour or so. now i've got a new ThinkPad T520, and if i start jack on USB at 64*2 i get hundreds of xruns in seconds. to run the same test patch without crashing, i have to go up to 256*2 (11.6msec). i've tried stopping a bunch of processes, and unloading kernel modules (mostly related to wireless and networking, and the hald-addon-storage polling), but it makes no difference. on both machines, i always lock the CPU's at max speed, and kill screensavers and DPMS. any help on where to look to solve this would be most appreciated! cheers! .pltk.