Hi ssunny,
The AD8232 is a very sensitive device so any noise can be picked up easily and amplified. You should first try to find out where the noise is getting picked up. You could first try applying a short circuit between LA, RA, and RL on the board and check whether the noise goes away. If that does not work, try putting the circuit in a shielded enclosure to shield from any possible environmental noise. You could use a metallic housing, or an easier solution would be to wrap a cardboard box in aluminum foil and connect it to ground. Also, please make sure that the board is thoroughly cleaned and that there is no residual flux on the board.
Try to give those a try and let me know if it improves.
Thanks,
Kris