Noise generator with LM318
Consider this circuit







simulate this circuit &ndash; Schematic created using CircuitLab

Your oscillation could be

1) thermal oscillation inside the Opamp, as the output current causes changes in the silicon heating, and the input bipolar diffpair becomes imbalanced; however the delta_V_out is 1 volt, so I doubt thermal feedback is the cause

2) how about 0.1 volts of I*R drop inside the battery, as the 10 or 20mA thru the Zener starts up, and the opamp amplifies that 0.1 volts by 10X to produce the 1 volt output? Yes. An internal resistance of 10 ohms or 5 ohms will cause this.