Hi Navin,
If you have instability it probably has more to do with design and PCB layout than it does with the rain. For example, C7, C8 and C9 should not be the same value and your input filtering is not very effective. C7 and C8 should be 1/10th the size of C9 so that drift effects are limited and differences in filter characteristics do not create a difference voltage at the input. L2 and L3 should be close to the connector followed by series resistance of 100 to 1k ohms. C7 through C9 should come after the series resistance.
Generally it is not a good idea to place any inductance in the supply path. If you want to reduce the noise from the digital supply use a 10 ohm resistor instead. The inductance on the supply limits current demand needed by the device and can create startup issues.
The other unseen problem is with PCB layout. To get a high level of performance an uninterrupted ground plane is recommended, especially around the analog section. A good guide for layout can be seen for the ADS1230 reference design:
http://www.ti.com/general/docs/lit/getliterature.tsp?literatureNumber=sbau125a&fileType=pdf
Best regards,
Bob B