  We analyse the capability of different type of perturbations -associated with
usual environment energy fluctuations of the solar corona- to excite slow and
sausage modes in solar flaring loops. We perform numerical simulations of the
MHD ideal equations considering straight plasma magnetic tubes subject to local
and global energy depositions. We find that local loop energy depositions of
typical microflares [$\sim$($10^{27}$-$10^{30}$) erg] are prone to drive slow
shock waves that induce slow mode patterns. The slow mode features are obtained
for every tested local energy deposition inside the loop. Meanwhile, to obtain
an observable sausage mode pattern a global perturbation, capable to modify
instantaneously the internal loop temperature, is required, i.e. the
characteristic conductive heating time must be much smaller than the radiative
cooling one. Experiments carried out by varying parameter $\beta$ show us that
the excitation of sausage modes does not depend significantly on the value of
this parameter but on the global or local character of the energy source.
