4K looks very clean, at least as far as what I have been able to view. I no longer have here a Sony server loaded with 4K content, nor the Red Ray player, similarly equipped that Epson had provided me. Thus, for viewing 4K on this Sony VW350ES, I have been limited to content from the 4K Download service. That content has some real compression. As a result, the source material isn't really clean enough to go hunting for subtle image noise issues.
Sony's one chronic issue is that it has more trouble with one speed of panning that other projectors. I've seen this on all the other Sonys. My test for this is the opening scene in RED where Bruce Willis is standing outside and the camera pans his suburban neighborhood. The trees literally vibrate. Oh, 3/2 pull-down and other MotionFlow options can tame it (including CFI), but for watching at pure 24fps, it is an issue. Fortunately, panning a little faster or slower gets rid of the problem. The RED sequence is the only significant one I've found, at least one that lasts more than a second or two.
Bottom Line on noises - both audible and image. As quiet or quieter than most other projectors around its price, and a good deal quieter than some. In low power mode, quiet enough that no one should complain at all. Image noise, only the panning, and that 3D performance could be better, but some of that is the inherent LCoS technology, so far only DLP seems to have the ability to be really free of crosstalk, whereas the Sony definitely exhibits some. Not bad though, unless you are really crosstalk adverse, in which case, sorry, there are no 4K DLP projectors yet.