AD7171-2 Eval Board Noise Test

Hi,

   I bought AD7175-2 Evaluation Board(EVAL-AD717x-2SDZ(Rev-E)) and carried out Noise test with two different configurations as below  and observed Signal variation

ADC ODR - 250 KSPS

My K20 SPI Clock - 6.25 MHZ

ADC Read / data - 10.4 uSec

1. Differential mode: Two inputs from same on board Reference source (ADR4450).

Test Set up as shown below

2. Differential mode: same signal feed to two inputs

why signal variation is 250uV in differential mode ? Please Explain.