When you brake or when you drive at high speed, it might be that the alignment is out. I didn't realize that, and thought my car was already busted, but turns out after I changed my tires (and redid alignment, of course), it all went away. It's way too quiet sometimes and I wonder if my car is actually moving. But of course all signs points to yes, except for the noisy tires and the annoying vibration.
EDITOR: Also I won a raffle, I have a new michigan tee. Another one to my many others. :)