My rear suspension was upgraded, but didn't really squeak. The problem isn't the Stazi endlinks, it has more to do with the cheap metal used on our car. I paid $200.00 to have a local shop (ATI Motorsports) re-inforce it. This shop also does the V8 conversion on the Focus as well and they've done a half a dozen CSVT's already, so they know the problem. Good luck with your ride, I'm sure you'll get it all straighten out.
Eric-break down and get those rear disc installed and/or get some new shoes back there

BTW, check out the cabins too.