I have a similar noise on my 3 dr 1.8. Prop has been removed. I've been advised that it is either one or both rear wheel bearings, or the diff. In addition to the continuous low rumbling, i also get a bit of vibration from the rear end, at very low speeds. Enough to make shopping bags rattle!! Check the bearings before removing the prop (unless the VCU is knackered). Hope this helps, Russ