What current values are prone to noise?
Your 1.3M + 10K divider has a source resistance (looking back from the ADC input) of 1.3M||10K ~= 10K. The Johnson noise from ideal resistors is likely negligible for your purposes-- 13nV/\$\sqrt{Hz}\$- so if your bandwidth is 1000Hz your RMS noise is 411nV or perhaps 2-3uVp-p. So if your full scale is 2.5V it would be good for about 20 bits, which is about the maximum that is probably achievable anyway. 

There are additional source of noise- noise current and noise voltage of the ADC, and leakage current. That depends a lot on the ADC- if unbuffered 10K is probably a good maximum number, but if you buffer it you could likely (depending on required accuracy) go considerably higher. 

So, for 'noise' I would look at the ADC requirements in relation to your accuracy spec, and also look carefully at the stability of (especially) the 1.3M resistor. Permanent drift of the resistance value with time under application of high DC voltage/moisture is not uncommon. You can get an idea of the stability with the resistor "load life" specification, but check the test conditions. 

Also, when you have high voltages on a PCB try to maximize creepage distances (for example by milled slots) and/or use guard traces to conduct leakage current away from sensitive nodes. A leakage resistance of 1G\$\Omega\$ in parallel with the 1.3M would cause 0.1% error.