rust? on gas tank

I have 09 X5, does anybody else see hideous discoloration on the gas tank underneath that looks like rust, can anything be still done about it since the car is still under warranty?
I did show it to the dealership couple of months ago and they said it is stainless steel which does not get rusted and kinda blew me off

Definitely take your car in for a pitstop inspection if it is still under warranty. This may have been caused by your car being exposed to chemicals on the road. Get the service mechanics to inspect the undercarriage.

Has anybody had something similar?

That looks like your muffler. Your gas tank is black plastic.

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Can't say if it will be covered, but I doubt it. They will say it needs to be rusted through to be claimed. IMO

This is very common, I have seen this on virtually every X5. With the factory hitch and cut out, the rust is especially noticeable. I ended up buying a can of black high temperature barbeque paint. It seems to work well.