Any time you do suspension work you run the risk of ending up w/ more rattles and squeaks. It's just the price we pay for a better ride... the tC was pretty bad in that regard IMO. If you can find what's rubbing in your dash, you may be able to put a little lube or piece of rubber between the pieces causing the noise when they hit/rub together. If your springs were installed at the dealer, you could always ask them to take a look at it.