There is some liquid or something sloshing around in the the back of my 05 sts. tThe car is running OK, I don't have a fuel odor so I know there's no gas leaking in. I check the trunk, nothing. Every time i start and stop the liquid sloshes forward. I think it may be the fuel tank that i am hearing, but I've NEVER heard it before. I've heard something about a fuel baffle?