Worn performance tires, out-of-alignment suspension, rear differential/joints can individually or collectively generate noise.

If you have performance tires and don't care about performance you will find that non-performance tires are more quiet.

If your suspension is out of alignment you could be "dragging" or "scuffing" a tire and that can make more noise than a well-aligned suspension.

These cars (the early model-years) were known to have differential failure. That would make a noise that changes frequency with speed, and can be louder or softer when you either step on or let off of the gas. You would probably feel vibration in the drive train but that would be hard to detect unless you had driven a car without the problem for quite a while.

Work through these in the order presented and you will find your culprit, though you should be aware that a coupe is a lot like a drum and noise tends to reverberate. If all is well and you prefer the tires you have, then your next move might be to Dynamat the entire car (at great expense to your wallet and car weight).

Between the stereo and my aging ears, It doesn't bother me. But then, my other vehicle is this so...