If your alignment is out even a bit, tires can very quickly develop a "diagonal" wear pattern, also known as "chopping." This makes 'em really, really noisy. A good tire shop could tell you if that's what has happened.
Unfortunately, once this wear pattern has developed, it cannot be corrected, even with a good alignment. The tires will work just as well, but the noise will never go away.
Contours in general, and SVTs in particular, are very touchy about alignment.
