OK, after monitoring the syslog, it turns out the problem seems to be related to the usb-uhci.c. The log gets filled with these messages, just about one per minute, and some of them, although not all of them, result in the audio blanking out for a second or so.
Jan 1 01:06:02 kernel: usb-uhci.c: iso_find_start: gap in seamless isochronous scheduling
Jan 1 01:07:02 kernel: usb-uhci.c: iso_find_start: gap in seamless isochronous scheduling
Jan 1 01:08:02 kernel: usb-uhci.c: iso_find_start: gap in seamless isochronous scheduling
When I had the USB stick connected to the first port and then switched it to the second (lower) port, i got gap-free playback for about 30 minutes. But the error messages above still kept filling the log. Then, out of nowhere, it blanked out at 01:37:02. And then at 01:44:02, '46, '48, '54, '58 and '00. Then I shut it down.
This problem was also described in this thread:
http://www.wl500g.info/showthread.ph...iso_find_start
Alas, they didn't seem to find a truly satisfying solution; simply switching the ports doesn't do it for me.
Heeeeelp!