Last week I had the brakes replaced in my 2001 Explorer Sport...new
pads all around, new rotors in the front, and turned rotors in the
back.  The first time I got on the interstate (60+ mph), I noticed a
vibration and a low-frequency noise coming from the front end.  The
vibration and the noise both increase significantly when I hit the
brakes.  Also, the vibration gets worse if I am turning slightly to
the left (still at highway speed only), but not to the right.  The
vibration is not constant; it only happens for the first 20-30 minutes
after I get up to highway speed, then it goes away and driving feels
normal.

I've talked to a few people, and gotten a different possible
explanation from each of them.

1.  separated belt in a tire
2.  bad bushing
3.  something wrong in the steering linkages...ball joints, tie rods,
etc.

I guess it could be any of these things, but one thing doesn't make
sense...why did this suddenly start after I got my brakes replaced?

Any thoughts on what could be wrong?