[V8] Replacement Battery and strange rumbling

[Eric Langheinrich]

Hoping someone can give me some guidance on a couple of problems I'm having. First and probably simplest is what to use for a replacement battery. As I've been shopping around, I found what seems to be a suitable battery at NAPA with the exception of the note to vent to the outside. That's difficult given the battery sits under the rear seat. 

The second problem I'm having is with a weird rumbling that seems to be coming from the rear of the car. The noise is only present when the car is in gear and only when moving at speed. Low speed doesn't cause the noise. When I drive over a bump the noise gets worse for a second, but then returns to the usual irritating noise. Any ideas? I've had the exhaust checked and have been told it's definitely not the exhaust. Is it the rear diff? Any other ideas on what I should check?