Yes the audio and sequence settings are both 48k 16bit.
I did just find a workaround.
I realized that if I exported only a very short section that includes the affected audio, it exports ok! So … I exported three seconds, it came out fine. Then I reimported that new quicktime, replaced that three second chunk with the new quicktime, reexported the entire sequence and now it is fine.
Weird!
So problem solved for now, but still of course would love to understand why that happens, to make sure it doesn’t happen in the future.
Hm.
Thanks 🙂