Ignore the silver covers on fuel treatement bottles? that's plain stupidity and carelessness
anyway, my car used to make a bubbling noise from the fuel tank, I check by lending the trunk an ear (190E) but it went away, I think it might have something to do that I was using a wrong fule tank cap, I got the right one now he he
the origianl, and I mean ORIGINAL, was so badly beaten that my car would leak fuel, so as a quick fix I got a oil cap that amazingly fit
waiting for it to occur again.