Crackling at high mixing levels, and with the fairly soft profile that you mentioned, is more likely to be a problem with analogue amplifiers or muting circuitry, not the DAC. I've had this loads of times with bad muting transistors (somehow, due to bad luck I guess) and read about similar issues others have had with relays.
A dodgy DAC would be more likely to produce harmonically distorted sounds or hard digital clipping/glitches.
I doubt the white noise floor will be altered by either (aside from during the pre-boot, muted stage).