my 67 makes a humming noise, almost like it has snow tires on, when driving at nearly any speed. Rolled the car in neutral down hill and still makes that noise. I think the car is a posi (just bought it a few weeks ago). Any ideas what this may be and a way to diagnose it? Also considering replacing body bushings, is there a step by step with a diagram anyone can share?

Reads like tire noise more than anything else. Try another set.

Reads like tire noise more than anything else. Try another set.

Yup! On the bushing replacement, do a search in suspensions, lots there. Make sure you get replacement bolts and washers, they usually don't come with the bushings.