Thanks for responding. The noise does not depend on whether I'm steering or how fast I'm going. Revs up faster with more speed, until it is overpowered by the engine noise, but back down at low speeds (decelerating or accelerating) I hear it again.

The noise will last throughout a trip, though some trips it is very quiet and some trips it is loud. Right away on the first backup out of my garage I will hear it (or not), and it will be the same for the whole trip.

I also suspect the CV joints in the axles. How can I test them? And what is a center bearing?

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84 300D "Soy Benz" - Soon to be WVO Conversion. 277K