I often forget the exact technical jargon to explain this issue -- see also: https://en.wikipedia.org/wiki/Image_noise
(salt and pepper image) -- but I know what it is.
I'm guessing that's a 1:1 (100% view) of the scan, and that's not the whole image. Notice that the noise appears only in the darker areas. Scanners are not much different than DSLRs, and that's a standard noise you'll get at higher ISOs. Scanners have the same concept, so I'm guessing the negative/slide is a bit dark or underexposed? That's the same as high ISO.
Heat and cold has affects on scanners/DSLRs, so if the issue is intermittent on the same scan, it could point to the scanner either getting too hot (overuse), or sadly breaking down. How old is it, how many hours of use does it have? Most scanners just seize up, but I've seen other components die as well. Capacitors, for example, can overheat, and it may cause this.
Some scanners have orange or white noise, and others can have red, blue, green, purple, etc. The exact color shown depends on different facts.
Also what brand/model is it? Hopefully it's something good, like Kodak or Nikon (assuming negative scanner), not one of those brand X units from the past 5-10 years. Or Epson for a flatbed.
Flatbed scanners have the same concept, but tend to use much cheaper parts, so any issue are amplified over negative/film scanning.
I've also seen scanners or software perform HDR-like behavior, and that definitely causes noise in shadows. So now the question is: What software is being used?
With various software filters, and various editing techniques, the noise can easily be removed, reduced, or at very least made irrelevant.