Hello, nice to be here. I have a mystery noise that I'm hoping someone can help me with.

99 Sedan d'Ville d'Elegance, 115,000 miles.

I have a, "flapping/thumping", noise that seems to start around 40 mph. Comes and goes. No vibe in steering wheel, new tires (2 weeks), recent rear brake rotors milled,
rear bushings replaced.

This noise comes and goes, road surface makes no difference...5 mechanics have been unable to hear noise when they drive it..but, of course when I drive it, I hear it...nope, not crazy, other passengers hear it too.

Help, please! I am somewhat fearful that something major is going on, but with mechanics unable to hear it, I feel like I'm driving a time bomb.

With appreciation,

Jan