Hi Petra,
Yes, I heard a tone like that yesterday. It was left ear, about 7 seconds, and what I would usually describe as a "blocking tone," except that it also had a sound like the ocean within it. Very unusual. Besides that, I heard a high tone in my right ear at the same time.

I don't know what to think the "seashell" element, much less what to think about the combination of these two tones.

Mary