My Vx has some loud rear wheel noise as well and I know the cause... It cause every thing is rusted away and there is a hole in the wheel wells. It also gets nice and humid in the car when it rains. I have replacement panels, I just have to get around to putting them on and repair the inner wheel wells.. God I hate body work.. It may be your problem as well....
Boy, I hope not! How did you check it? One way I can think of is to remove the covers below the rear side windows for the speakers next to the rear seat. Can this rust hole be seen through this area or does the side panel behind the rear seat have to be removed? I would sure like to find out! Thanks for the info.
If you have low or reduced rolling resistance tires on your VX (for better fuel efficiency) that may be the source of the noise. I think LRR tires tend to have harder rubber compounding, and that transmits more noise. Civics don't have a lot of noise absorbent material anyway and I suspect (but don't know) that the VXes left some of it out to reduce weight.
I used to have Goodyear Invicta GLR tires on my VX. They were by far the noisiest tires I've ever used on any car, ever. I did think for a while that the rear wheel bearings were about to seize up, but it was just the tires.