This time CapXon are the culprits.
One of my Linksys WRT54G routers started to emanate an annoying hissing sound. I figured that some of the capacitors must have been dying so I opened up the router.
These two capacitors need to be replaced with some low esr capacitors.
I used some Panasonic FM 220uf 25v DIAMETER: ~8mm HEIGHT: ~8mm DIGIKEY PART NUMBER: P12383-ND
Once replaced the router was silent.