weird noise-anyone familiar

3 times in the last 2 weeks I have heard a "boom" that sounds like it is coming from the right rear quarter panel area. Gas tank???? Yikes!! The first time I heard it I thought someone threw something at the car. Has anyone ever experienced this? Any good guesses?

Thanks,
Art
1989 325IC

I can't say I have... But If it sounds like a rock hitting the quarter panel (and not a clunck you can feel in your seat) then I think you have your answer. Experiment and note what tank level it happens at, and don't piss off the local kids
But really, if it's the tank expanding/contracting because it has a dent in the underside, it will make very different sounds depending on the quantity of fuel in it. Think pinching a soda can when it's empty vs full. if you notice a pattern involving fuel level, and your fuel tank looks visually okay, you're probably okay.

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1989 - E30 - M20 - Manual. Approximately 270,000 miles
2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles

I found it !!!! It made me smile when i figured it out because it was by accident that I found it. I have been a motorcycle mechanic(usually service manager) for half of my working adult life, I'm 48 yo now. I have always told other mechanics when they are "wracking their brains out" trying to figure out a problem...."ITS ALWAYS SOMETHING SIMPLE"

Well tonight I pulled into my garage, went around the back of the car, as I walked by the passenger side I noticed the passenger door window was sticking out a little bit, it was catching on the top.....I pushed it in a little bit and "BOOM" it popped into place!!!! I had to laugh....that was my "gas tank is going to blow me up" demon!!! Now I can work on the other 17,500 projects I have going instead of trying to figure this out tomorrow!

Thanks for your idea Earendil....I would have been looking for a dent in the gas tank or pinched breather tomorrow for sure.

Art

btw-just noticed you're in Wa too.