Tires: noise in rear, nissan sentra, couple blocks

Question
I drive a 99 Nissan Sentra, and there is a noise that comes from the rear. It is usually after my car has been sitting for a while, usually a couple of hours at least. The noise begins when I start driving.  It sounds like it's the tires (like a rubbing noise). However, once I've driven a couple blocks, it's gone, making it difficult to pinpoint. I recently checked the air, so I know it's not that. However, if I haven't been parked for long, and I start driving, the car doesn't make the noise. I'm not sure if it's even the tires - just wanted to throw it out there. Thanks in advance.

Answer
Jarvis,

Tires do develop flat spots from sitting in one location.  The longer the tire sits, the larger the flat spot.

Driving a few miles heats up the tire and the flat spot gradually disappears.

Try this:  Add 5 psi to the tire pressures.  If the problem gets better than it was flat spots.  If not, it's something else.