I'm getting a rattling at low speeds or if I'm starting out in 2nd gear,any time there's engine vibration, downshifting/ rolling starts? Sounds like a heat shield or something.

I looked under the car, didn't see anything but not sure where to look exactly, it's hard to place where its coming from while driving...

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Do you have an aftermarket exhaust? Some of them have piping that touches the rear axel or springs and makes an odd sound at low speeds or when turning.

I was having a similar sound to what you're describing, and it turned out to be my power steering belt was wearing out.

I dunno if any of this helps.

 

It sounds more like it might be up front somewhere.

 

Take a close look at the exhaust, back near the rear suspension. On the xB, there is a short bracket that runs across the bottom of the exhaust channel. The xA may have it as well, but I'm not sure.
This bracket is pretty flimsy and can get bent upward if you accidentally ran over something recently. It may not be touching the exhaust all of the time, but under load (such as during acceleration), the exhaust will move around a bit and may be coming into contact with this bracket.
It happened to me a while back and scare the **** out of me! I thought my trans was coming apart or something!