Hums Like A ?

My 8 3/4 Has 323 In It But When I Coast To Stop A It Hums Like Wowowowooowwooo Sounds Like A Slow Lathe It Has Over 300,000 Miles On It But Still Lays A Sweet True Dbl Stip At Will Changed Beirings And Fluid But Still A Hums A Like Champ Any Info Would Be Mucho Appricato Do I Have To Rebuild This Thing Or Ride It Till It ?