It's easy enough to verify if it's the flex disc or not just by getting it on a hoist. There actually is an inspection interval for the front flex disc, I believe it's every 60,000 miles it's supposed to be inspected. It could also be what is called the "mid ship" or "mid shaft" bearing. The car has a 2 piece drive shaft, and this is the bearing that supports the middle of the driveshaft. OR it could also be the mid ship bearing support, which is a metal support for the middle of the driveshaft which also has a rubber collar inside which is known to wear out.
To inspect the front flex disc, just get it up on a hoist. Make sure the parking brake is NOT set. Grab the driveshaft and twist it back and forth (at the front of the shaft if possible, sometimes there's not much room, depending on the exact model, and a helper needs to twist the driveshaft back near the differential while you observe the front flex disc). While the shaft is being twisted back and forth, watch the 2 sets of bolts that hold the flex disc to the driveshaft and transmission (3 bolts for each job).
When twisting the shaft, there should be only a small amount of motion between the 2 sets of bolts. Also with a good light, you should see that the rubber surrounding each bolt is intact. If the rubber around the bolts is gone, you know right away it's junk.
To inspect the midship bearing and support, grab the driveshaft as close to the middle of the shaft that you can (usually from the rear of the shaft, you can get closer to the middle fron the rear) and try moving the shaft up and down and see if you can detect any movement.
To do either of these jobs is pretty involved, it almost has to be on a hoist. You need to be able to spin the driveshaft to access all the bolts, and it really helps to take off the transmission mount, which involves having the car in the air, and holding up the transmission with a transmission jack or pole jack (screw jack) of some kind.