You really need to read about SPICE analysis methods and setup for noise analysis.
Noise analysis is a small signal AC analysis, it doesn't use e.g. sin() source which is only for transient (large signal) analysis.
Small signal analysis (gain, frequency response, noise) of nonlinear circuits, e.g. amplifiers depends on suitable bias point. As a first guess, you can set Vin1 DC level to vdd/2. Depending on the MOSFET asymmetry, you may want to adjust the bias level to get vdd/2 DC output bias. Or use a self biasing test setup with DC feedback.
In any case, you should check the operation point after setting inverter bias.