Car's been sitting a lot for a few months and it's the middle of winter in MN. Finally got it fixed enough to do some highway miles and I'm getting this fairly pronounced rotating rubbing/friction noise, about 6 times per second at 70mph, and isn't very present below 50. Sounds like it's centered between the front seats. Stops when I let off the gas. I'm assuming it's the U joint or shaft bearing but I'm a hobbyist at best, anyone got other ideas? Any way to test if it's a worn gear? It has 300k miles on it, no idea when the driveline was serviced last but it was always serviced at every interval at Ford. Thanks.