Part of this is due to the human hearing system: You can't hear people talk at a rock concert, but you can hear them whisper in a library. The other part may be due to some compression at some point of the audio chain. Compression boosts the quiet parts - including the noise.
Is it normal to have a background noise like shhhhhhhh in holes of a recorded audio track ?
When the sample starts playing the background hiss is cut. When the instrument stop playing the hiss reappears.
My music is already a bunch of noises and this hiss is not necessary...
I must say that I discovered this phenomenon when the volume and gain of the track were set to very high.
The card is a MAudio 24/96.
There are various things that could be causing it. If it is really loud and bothers you, try turning off all your outboard gear and then each piece of equipment on its own and then build up the combinations. I say this as I had a similar problem with a Lexicon reverb. I actually solved it by Gerry-rigging the plug! Not to be recommended :>)