How to add noise source in circuit simulation under cadence?

Normally, when we simulate the oscilaltion of an LC oscillator, we would add some excitation such as a pulse signal to the oscillation node to excite the oscillation. However, that is not the real case.

Now I tried to simuate the build-up time of an oscillation excited by noise and input signal seperately. How could I add the noise source or equivalent exitation source in the simulation?

Thank you.