I don't think it is dither. Dither is only toggling of the least significant bit, which, with normal gain, is not audible, and would be a pure tone, not a "shushing" sound.
Even with a digital master recording some analog amplification of the microphone is involved, and might contribute some noise. More likely, the analog stages of your digital source may be noisy.
Even with a digital master recording some analog amplification of the microphone is involved, and might contribute some noise. More likely, the analog stages of your digital source may be noisy.