Loud howling noise at rear of my 2002 Honda CR-V?

I just got a 2002 Honda crv yesterday it does have problems with it. Like squeaky brakes/ needs a battery (I think) or a cleaning of the battery posts. That's what the guy told me, an such. But it's making a howling Noise at the rear of the car. It almost sounds like wind. Low pitched. I'm not too sure what it could be? I have to get quite a bit things fixed but just wanted to know if anyone knew, so it would help me out! Thanks:)

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