ADS1299: There is spike noise in ads1299 data acquire

Part Number: ADS1299

When I short(outside) the input of the ADS1299, sometimes a spike noise like the one shown in the picture appears. Could you please explain why this happens and how I can resolve it?Thanks!!!

The output code is -1000 apprioximately when ads1299 is working well, but the output code gose to -8000 approximately when the spikes appear, and the spikes may come to -4000.(I mean these spikes come together with large output offset of ads1299)