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I bought an Ender 3 S1 about a week ago. Everything is going pretty well, I have it dialed in, good prints. It's really quiet when printing... EXCEPT...

During higher-speed Y-axis traveling (bed moving front to back or back to front) the travel is loud. Almost a "woop" when it's moving. Kind of sounds like when you rapidly move a zipper (although a little lower pitched than that). Regular printing seems really quiet, especially compared to all the "singing" of the steppers in my last printer. But this loud Y-axis is a bit bothersome. To clarify - it seems like non-printing travelling is doing this - not regular y axis travel during printing.

I've taken it apart. Print bed on its own moves smoothly and easily, no wobble, very quiet. I didn't find any loose fasteners.
I get some noise when the belt is attached and I manually move the bed (with unit off or steppers disabled) I can't see that the belt is rubbing on anything. Belt tension doesn't seem to affect the sound. I took off the bottom panel and tried some electrical tape around the edges to insulate the panel from the rest of the printer. Didn't seem to help.

I'm using Cura as a slicer. I originally set print speed at 50, (35 walls, 25 top and bottom, 50 infill) and Cura automatically wants to set travel speed in this case for 150. Even at 100mm/s travel Y is quite loud. Closer to 75 it's a little better, but still quite jarring.

Checking again - moving x-axis manually makes the same kind of sound, but softer. I'm beginning to think the body of the printer is acting as a sounding board when Y-axis moves - and that's amplifying the sound.

If this is just the way it is, I'll deal with it. I'll just have to come up with an enclosure to deaden the sound, I guess. But if there's something I'm missing, I'd appreciate any advice.