This may sound odd, but perhaps something HAS died. I've seen photos
of multiple instances where mice have crawled into a computer and
gotten stuck (attracted to the cozy-warm interior I suppose). Just for
grins, you might open up the computer case and take a peek inside. If
that's all clear, it's also possible that a critter has died inside
your wall or something. Check nearby forced air ducts, check any
plumbing penetrations, check around outlet covers, etc. If it's really
bad and you can't find it, it may be worthwhile to actually try to put
a small hole in the wall where it's strongest and attempt to look
around inside with a small mirror and a flashlight.