Hi Sivanantham,
I'm sorry for the delayed response. There are a number of possible noise sources, so it is difficult to pinpoint a single source. You mentioned the power regulator, and it is possible this is causing some issues as the switching frequency harmonic may alias back into the passband of the ADC. The ADS1232 has good power supply rejection, but this could still be a part of the noise issue. We recommend to use a linear, low noise regulator.
It would also be a benefit to have the differential capacitors closer to the ADS1232 input pins. It might also make more sense to have the ferrites on the other side of the filter. Component selection may make some difference as well. Capacitor grade is especially important. A high grade of cap is much more stable and has a lower noise dielectric.
A bigger concern is your basic layout and where return paths are forced into less desirable locations. Due to the nature of how the ground return flows, it might make more sense to use a common ground. The grounds are common anyway, so why split them only to bring them together again. Please review the information in this section:
Best regards,
Bob B