Without hearing it, it is hard to pinpoint. But, without knowing exactly what/where it comes from, elimination my be the only recourse until you have more information.
Wheel bearings: Put the car up on jack stands first. Then rotate each of the front wheel/tires to see if that will create the sound. Also, push and pull (wiggle) the tire to see if there is any give in the bearing. Then rotate the wheel about 1/8th of a turn and try again and keep doing the push/pull/rotate until you've gone 360? of rotation. Repeat for both front wheels before moving to the rear wheels: same procedure.
How are your brake pads? are they wearing evenly or is there more wear on one end of the pad(s) that the other (assuming the pads are not worn out, i.e., metal on metal)?
Next, start the car, put it in gear, and let the clutch out and listen while the engine idles. Go thru all of the gears and see if the sound appears.
Try the brakes
Try turning the steering wheel from stop to stop. Any gear noise/pump whine?
NOTE: Especially in the lower gears, and in the 90 to 92s, the angle of the helix cut in the transmission gears was such that they made a low growling sound whenever under load, which is normal for those early Zs. It isn't that, is it?
Well, let us see what you discover after this experiment: either the sound is re-created or is it now gone? Either way, that is good information to have.
Let us know what you find or don't! 