All choked up

[MrChumble]

For some reason I'm getting horrible choke in CSS. It doesn't happen in any other games, just CSS. I've tried changing rates (between 15000 and 2500), capping fps at 60 and matching my cl_updaterate to that. Also tried updaterate and cmdrate between 20 and 101 in various combinations; shutting down all other internet based programs; turning off my software firewall (ZA); making sure port forwarding is set up properly on my router. In a fit of desperation I even tried RTFM'ing.

I'm fresh out of ideas, can anyone help?