I, too, have had this question! I purchased an EX-4S from Costco before Christmas (2020). The bike was silent for multiple workouts for multiple family members during the first week. Then, into the second or third week, I started to notice a "clicking" sound (not necessarily the perfect description for it) coming from the flywheel--not the pedals. I checked on the tension of the screws on the flywheel and found them to be super tight. My only conclusion was that the sound might be coming from some bearings in the flywheel area.
When I reached out to Customer Support, the first person was concerned and offered to send new pedals, but invited me to provide a video. After doing so, my question was escalated with the attached video. After a little back and forth, I was told that a supervisor said that the sound (which had become a constant sound ... much more than occasional "clicking") was normal and that the bike should not be expected to be silent. This surprised me because it seems like bikes with magnetic resistance would be virtually silent. (And the bike wasn't cheap!)
Nothing else about the bike performed poorly during the first 5-6 weeks, so I did my best to accept the sound. But, after talking to my local Costco, it was suggested that I return my first bike and replace it with a new one. I did so a few weeks ago. For the first full week, the new bike has been completely silent for multiple workouts across multiple family members. But, after finishing a workout yesterday, I thought I heard the beginning of that "clicking" sound from the bearings--almost identical to the sound heard in the video in the original post.
So, it would be good to know if this is just a "Costco bike (EX-4S) thing" or if others who own different Echelon bikes can support the message from the Echelon supervisor that the sounds from the flywheel area are normal and that the bike should not be expected to be silent. I love the bike and the workouts. I haven't found the sounds to affect the bike's performance. But I also don't to be left with an expensive bike that is afflicted with a unique problem that may not have a solution.