Wireless traffic stomps isdn traffic on gateway machine
 

I have an odd problem, and not one I can pinpoint by myself, so I'm asking for some pointers.

I have a gateway machine that I use for both wireless freenet and isdn internet connectivity.
The wireless card is a cabletron roamabout, running orinoco_cs 0.13e, connected through an ISA-PCMCIA connector and the isdn card is a NetJet-S pci card.
It was running the 2.4.20 kernel previously, and worked a treat. Everything worked fine.
When I tried compiling the 2.4.21 and 2.4.22 kernels though, I noticed something odd. Whenever I downloaded off the wireless, the speed of my isdn dropped significantly.
More than say 100kB/s worth of wireless traffic, and my isdn downloads - which were sitting on 8kB/s solid for a while were suddenly dropped down to 0.1kB/s. The same doesn't hold true for the reverse. Also note that while wireless downloads stomp isdn downloads - upload traffic remains unaffected.

Now at the time, I passed this off a bit.. figured I must have done something odd in creating my kernel - perhaps ticked some load balancing box somewhere. I'd also checked the I/O and IRQ's to make sure there were no conflicts and couldn't find any reason for it. Then I'd given up and gone back to the working 2.4.20 kernel.

The other day I decided to update the box and I installed the latest Knoppix 3.3 (Nov03) on it (using their nifty install to hdd feature to get a nice debian setup) - and what should surface again with the default 2.4.22-xfs kernel is this issue with wireless stomping isdn traffic.

I have no idea who to ask about this.. and short of building a 2.4.20 kernel to use I have no solution - so anything you can suggest is welcome.