Pressure fluctuations and air bubbles

[environment]

We are experiencing some problems with our Agilent 1200 Quaternary pump/1200 series vacuum degasser. We experienced contamination problems with the degasser and it was taken off line. Helium was used to degas the solvents [acetonitrile (pump B)/water (pump A) used in a gradient]. The pressure began fluctuating and air bubbles were observed going from the MCGV valve to the pump. The bubbles were also coming out of the detector and spikes were observed on the baseline. When the degasser was put back on line, the problem went away. Any ideas as to what may be causing these pressure fluctuations and bubbles when the degasser is replaced with helium sparging?

thanks

[Consumer Products Guy]

It sounds like sparging was done done sufficiently, or that air was able to get into the lines when you reconnected after removing the degasser...