Low speed grinding noise

[subieworx]

New noise has started over the past couple weeks. It is a sort of grinding or roaring noise that is present at low speed when going straight. It sounds very similar to tire noise, but is not. It is difficult to tell where the noise is coming from, but I would guess the center of the drivetrain.

If I start from a stop the noise will begin around 8mph and continue to about 17mph where it then stops. If I accelerate through this range of speed, but am turning there is no noise. I don't seem to hear this noise at other speeds.

ANy ideas? Searching didn't reveal much.