Sound of fuel sloshing heard loud & clear in cabin, cause for worry?

[Mervyn]

From inside the cabin, even in the driver's seat, I could hear the sound of fuel sloshing in the fuel tank. It's even louder in the rear seat, and my passengers have been pretty amused! The slish-slosh sound is very apparent from a full tank right down to 1/5 tankful of fuel. I could also hear the return fuel sloshing back into the tank. No, my hearing is not exceptionally good, just normal.

Is this normal, or does this point to something undesirable?

Any advice is appreciated, thanks!

Mervyn
1983 W126 (280SEL)