Shutdown p5000etch SNF 2010-04-25 21:57:06: etch fluctuations due to DC bias and He leak

I have noticed strange etch rate fluctions in the past. This has been very intermitant and has not correlated with any fluctions in gas flows, pressure, RF power, magnetic field, or He leak rate. Tonight I observed this again, quite apparent on the EPD showing a drop from -1 to -2 over the course of 10sec. It was correlated with a drop in the DC bias from -450 (+/-10V) to widely flucting DC bias between -50 and -120V. The helium leak rate remained below 3sccm during this.
Then, on another wafer, the He leak rate of ~9sccm caused error. These two issues seem unrelated, but its hard to say at this time.