OK, I hear what's happening. As you say Hans, there is a faint tinselly, high-frequency wheezy noise coming mainly from the left channel on the front of the mf (vel 76) F4 sample in the Appassionata Strings_sus patch (In this register I think we're hearing only the VI-20_sus_Vib violins, no violas or cellos.)
The patch is programmed in such a way that the noise only sounds when you move to F4 from another note - if you play a series of F4's the noise isn't there, which explains why you can't hear the noise unless it's in the phrase!
Personally I don't find it too disruptive - add a little reverb and I doubt anyone would notice it within a piece of music. However, it doesn't sound very musical and I imagine it could easily be eradicated by VSL by a bit of sample substitution. Just my opinion!
Do VSL tech staff agree there's a problem with this sample?