I have the silent runner
It should be silent. I know it isn't silent if you don't put the spacer on - so could it be it isn't completely assembled? When I first got mine I didn't have the front and back pieces pushed onto the track firmly enough - meaning there was a gap either side of the clear plastic joining strip on the running track, and the wheel wobbled a bit with a sort of scissors action. Once it was pointed out to me, I pushed the front and back on firmly and there was no gap and it ran perfectly.
When you put it together, there should be a bolt that goes through the hole in the back, then a metal tube - the spacer, then the end of the bolt goes through the hole in the stand, then the wing nut on the back. I found adjusting the wing nut slightly made the difference between it running a bit stiffly and running really well. But adjusting it too much can make it loose and wobbly.
If you've done all that right then maybe it's a faulty one. They have ballbearings inside the back panel that make it silent - so it could be faulty ball bearings. In which case I would ask the seller to replace it, if possible.
If you've checked everything is assembled properly I would definitely contact the seller and explain the problem, as you have above, and let them go through all the checks (assembled correcetly etc) and then the onus is on them to offer to replace it if it sounds faulty. Although sometimes they won't after 28 days.
If it helps I did a video review of it, and at the end are pictures showing how it is assembled. If you fast forward through the video you can see it being assembled/labelled. If you watch a bit of the video you'll see how it should run silently.
https://www.youtube.com/edit?o=U&video_id=VFussTX5PuE