Testing the AD1940 and ADAU1446 Evaluations Boards, with a simple circuit (in directly to out), just using one channel (mono), I put a 1Khz sinus at input, and check the output test pin (with no loads). Let's see the signal. I've noted a noise over output signal at 45 Khz (AD1940) and 22 Khz (ADAU1446). Both running at 48 Khz (sampling rate). So I need a help if is normal, and how to avoid this.
This is due to the digital interpolation filter in the DAC. It is part of a tradeoff between die area, power, group delay, and performance. Note that this is well above the audio frequency range and it is about -75 dB relative to the operating level of the system; therefore, it is inaudible. If you want to remove this component, then use a steeper analog filter after the DAC output.