Dear Tamar,
In MATLAB I recommend the following (this assumes a monaural sound (one column vector), so you have to adjust it for stereo sounds):
[insig,fs] = audioread(file2load);
Ma_amplitude = max(abs(insig)); % maximum absolute amplitude
dB_below = 100; % dB below the maximum amplitude to look for...
Mi_amplitude = Ma_amplitude*10^(-dB_below/20);
idx_i = find(abs(insig1)>=Mi_amplitude,1,'first'); % first sample with absolute value above Mi_amplitude
idx_f = find(abs(insig1)<=Mi_amplitude,1,'last'); % last sample with absolute value above Mi_amplitude
insig_cut = insig(idx_i:idx_f);
I hope it is intuitive. If you are conservative you can set the "dB_below" to cut amplitudes 100 dB the maximum value but it could be good enough to use 60 dB of 40 dB, just make sure you don't get clips when reproducing the resulting files...
Cheers,
Alejandro