Aluminum frame; sealed roller bearings; carbon fork with (I assume) aluminum steerer tube.

I'll try the rough-up and taking it apart again. Once I figure out the brand of the stem, I think Park Tool has torque specs for different brands.

The bike's only got 5K miles on it and has been well cared for, so I'm sure nothing needs to be replaced.

But the creaking does get to you after awhile. Funny thing--it usually doesn't start until I've ridden 10 or 15 miles and is worst when pedaling uphill.