I searched and did not find anything that sounded like my problem. My 97 D1 with 157K just started making a strange growling noise when going above 50 MPH and letting off the accelerator. The noise seems to be coming from the front. Slight vibration as well when accelerating, but not felt through the steering wheel. I looked at the front drive shaft this morning and it looks normal. I think I will remove it and drive without it to see if i can issolate the noise. Is this safe to lock my CDL and drive on the highway with the front drive shaft? Any ideas on what could cause this.