2002 Maxima Steering Shimmy Above 50 MPH

I just purchased a 2002 Maxima SE with 45,000 miles on it.  It had new
brakes, rotors, and pads at the time.  I thought that the tires were
mis-balanced so I had them re-balanced but I still have a slight
shimmy in the steering above 50 mph but below 70 mph.  I don't know
what this is, but I was thinking of going back to the dealer to have
them figure it out.  Any suggestions or has this happened to anyone?
I was told possibly a bent rim or bad wear on the tires.  Any
suggestions would be appreciated.

-Anthony
2002 Nissan Maxima SE