Violas and cellos have whistling noise in high "yellow" register; is that normal?

I don't play strings, but when I was experimenting with how high the stringed instruments could go, I noticed a shrill, irritating whistling that appears starting at about Eb5 on cello and viola. I know those are marked as difficult to play (the yellow color), but is it normal for strings to make that noise? If not, maybe there needs to be a fix. I've noticed this on the General HQ and GeneralUserGS soundfonts.