A mystery! I need help with disappearing oil.

I decided to change oil in my '18 718 after 500 mi. I decided on 5W-50 Amsoil full synthetic an approved viscosity). Manual says 6 qts, which I assume includes filter.

I drained the oil, replaced the filter, and added 6 qts Amsoil. After driving a couple of miles, I got a dash message that said I have too much oil in engine and that I should get it checked by dealer pretty soon (didn't sound like an emergency). I tried to suck out some oil thru the filler hole, using a flexible plastic hose abt 1/4" diameter. No luck, not a drop. Phooey, sez I (or something like that).

So it's back up on the hoist, remove drain plug over a clean container. All that would come out was 1 cup (1/4 qt.). SAY WHAT?!

I tried blowing gently into the filler neck, no luck. I tried vacuuming from the drain plug. No luck. I tilted the front of the car up about a foot, no luck. Then the rear up, no luck.

So I went out for a 10 mi. drive at speed to see what would happen. I was on the expressway, so I used earplugs. No signs of anything amiss (e.g. smoke from exhaust). But when I got off the expressway, I took out the earplugs and noticed a loudish whine, proportional to RPM. Never heard it before. I guessed it might be oil pump noise. Or? Manual says that too much oil can cause cat damage. Oil temp and oil pressures were normal.

So, guys, where's the oil? It's trapped in the engine somewhere. Where? I assume this is a wet sump engine. If not, is the oil trapped in a tank?

Obviously, I can -- and will if I can't get some oil out -- call the dealer. But really! Oil's gotta be in there somewhere.

I didn't used to believe in black magic, but now, I'm not sure.

Help!