We show through numerical simulations that different kinds of noise ha
ve different signatures in the statistical distribution of the intensi
ty peak height as a function of delay time in the turn-on of class-B l
asers. Simulations are carried out specifically for a CO2 laser and ar
e compared to the experimental results of H. Grassi et al. [Phys. Rev.
A 50, 805 (1994)]. Full qualitative agreement is found with the exper
iment. These results confirm that noise on the control parameter has a
larger influence on the laser behavior than the intrinsic fluctuation
s. A physical interpretation of the role that the different physical n
oise sources play in the system is offered.