noise - ADC outputs random values to constant input

I am using ADC (ADS7822) from TI and I have some strange behaviour with it. Below diagram explains the voltage inputs and connections.

I was reading strange values with this setup.

1. 
   

   I removed signal and provided a fixed DC voltage of 2V to PIN 2 (+In). I assume I will get some value for wich the MSB will be almost close to each other on each samples. I am comparing 400 samples at a time. But I receive dynamic outputs from the ADC wich has all possible values.

   
   


2. 
   

   The first sample is always zero (surprising). I always get sampled values for 2V from the 2nd sample onwards.

   
   


3. 
   

   Even if I don't provide and signal to PIN 2 (floating) it still outputs some data. I am providing clock and ss low so I assume it will sample noise if no signal is present. But the output should be close to each other. I receive all values from FFF to 000. I don't see such source of noise in my system.

   
   

Can someone suggest any possible reason for this behaviour?