i can feel/hear rattling around headset area
when i'm riding, especially over bumpy roads, i can feel/hear some rattling around the headset area. i know for fact it's not the stem/handlebar because i've already tightened them. also, when i lift the front wheel and try to shake the headset up and down (by holding onto the handlebar), it moves up and down very slightly (very little).
is this something that is normal? on smooth roads i hear no rattling.
I thing you self diagnosed it - you need to adjust and tighten the headset. Headset noise and rattle is not normal.
For threadless headsets: http://www.parktool.com/repair/readhowto.asp?id=65
For threaded headsets: http://www.parktool.com/repair/readhowto.asp?id=127
just got back from lbs. forgot to mention i installed a new stem previous to this problem. mechanic said i need another spacer to leave a small gap at the top.
Yes, threadless headsets need about 1/8" (3mm) gap between the top of the stem and top of the steer tube. The gap is needed to ensure you can pre-load the bearing system without bottoming out. Anyway, sounds like it's fixed.