Well, generally, rear end, driveshaft and brake noises stay consistent with road speed. So, clutch in and still there? That isolates the search. Outer axle bearings tend to moan rather than make a rotating sound. inners tend to grind as they disintegrate. Rear gears tend to whine on accel or coast at particular road speeds. Tires tend to rumble as they age, particularly the factory summer Pirellis on BBP or TP.
In and out with the clutch engagement? Transmission and clutch likely culprits.
Variable with rpm? Engine and accessory drives.
Why are you pursuing lemon? What's wrong with the car that's led to that? Is this the only issue? Maybe record it for us and post a vid.
2014 Premium GT, SGM, Brembo, Auto, Tech, Comfort, etc. GT500s, Steeda UCA, VMP auto N/A tune. 100 shot nitrous on BBR tune. Best e/t 11.38 at 120.85
2012 Premium GT, Candy Red, Brembo package, 3.73, MT82, Comfort, Tech, et al. Procal tune, Roush UCA, UMI poly LCA, GT500s, Steeda red bracket, Hoosier 28x10x16 bias drags. Best e/t 11.91 at 115.23 RIP