Something wrapped on the driveshaft would change pitch with road speed. My gut's telling me it's another incident of a collapsed bearing in the trans. Since it's all gears, that suggests mainshaft or output shaft. Does it change when you put the clutch in at speed? If it does, then the problem may lie in the trans, if it doesn't, then it's in the driveline, brakes, wheel bearings, since those are road speed related when noisy.
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