I am testing a capacitive load under different voltages. At certain voltage levels I get alot of noise. However, when a resistor is used in series with the ground, the noise is suppressed? Why is this?

 

Give us an idea of what you think the reason is, as only you know the actual circuit and signal conditions.

 

Could it be high frequency oscillation that is stopped by the resistor?

 

Could it be high frequency oscillation that is stopped by the resistor?

You've already stated that it apparently does.
But we are not clairvoyant.
We can't tell you why without a schematic of the complete test circuit and conditions.