adding phase and amplitude noise in my ideal frequency modulated signal

Hello, I want to add amplitude and phase noise (Both white gausian noise) in my frequncy modulated signal. How to do this. After that i need to see how the output is changing after adding white gausian noise. init_phase is zero so i can add phase noise there only. Moreover, fs = sampling frequency, fc = center frequency, x = output of signal generator, t = time vector, init_phase = I shoud be adding phase at init_phase. Thanks

function [st] = vco_function(fc,fs, bw, x, t,init_phase)
%VCO_FUNCTION Summary of this function goes here
%   Detailed explanation goes here
if nargin < 6
    init_phase = 0;
end

if (fs < 2*fc)  
    disp('Error: fs must at least 2*fc');
    return;
end

int_x = cumsum(x)/fs;
st = cos(2*pi*fc.*t + 2*pi*bw*int_x + init_phase);   % Frequency modulation formula

end