Channel Noise with Bucket Test

[Atlantico]

We have the active two system with ExG1-8 and A1-16 channels.

We have done the one bucket test to all channels (salted distilled water inside, motionless electrodes) and we are getting these spikes and oscillations as shown in the figure bellow. What could be the cause to this?
Time axis in seconds, amplitude microvolts , application EEG processing Thanks

[attachment=0]BioSemi16Mai14OneBuckeTestLeadsTogether_marked_comp.jpg[/attachment]

[Coen]

Small "pops" in the signal are quite normal during the first 5-10 minutes of a bucket test. They are probably caused by traces of pollution on the electrodes that go into solution (and therefore change the galvanic half cell voltage of the electrode). With good clean electrodes, the pops usually disappear after a few minutes soaking in salt water. Another reason for pops are electrode tips momentarily touching each other.

Best regards, Coen (BioSemi)