Mux for ultra low noise pre-amplifier
I think your noise requirement is unrealistic. Do you really have a preamplifier and ADC that gives you more than 24 noise-free bits?

You mention DC signals; what is the noise bandwidth that you care about?

Let's look at the datasheet for the part you mention. There's actually lots of noise-related information there; you're just not seeing it.

The on resistance of the ADG1401 is on the order of 1 &Omega;. This means that you can pass no more than 1 &micro;A through it before you create a 1 LSB offset in the measurement.

Leakage currents are on the order of 3 nA (typical over temperature). This means that your input impedance can be no more than 330 &Omega; without creating a 1 LSB offset in a measurement.

Isolation is shown as being on the order of -100 dB at frequencies less than about 10 kHz. This means that 100 &micro;V of your 10-V signal can leak through to your preamp, perturbing the measurements of the other input channels.

THD+noise is given as 0.008% at frequencies as low as 20 Hz. This is an error of 800 &micro;V on a 10-V signal.

Finally, the ACPSRR is shown as being -90 dB at best. This means that you need to keep the noise on the power rails to less than 31 mV in order to inject less than 1 &micro;V of noise into the measurement.