Concatenating cuts off length of overall .wav file (when summed)

 loc = 'insert dir of where you placed your files here';
 filenames = {...
    [loc, '\', 'audio1.wav'],
    [loc, '\', 'audio2.wav'],
    [loc, '\', 'audio3.wav']};

 concat = [];
[y, Fs] = audioread(char(filenames {1}));
silence_length = 30; %%[sec]
silence_block = zeros(silence_length * Fs, 1);
pip_length = 0.2; % [s] length of each pip
number_of_pips = 3;

 for i = 2:length(filenames)
    [y, Fs] = audioread(char(filenames {1}));
    frames_to_crop = pip_length * number_of_pips * Fs;
    y = y(frames_to_crop+1:end);
    concat = [concat; y];
 end;

 output_file =  [loc, '\', 'concat_cond123', '.wav'];
 audiowrite(output_file, concat, Fs);

Trying to concatenate 3 .wav files, each with exactly 13:20 in length. However, when I get the resulting 'concat_cond123.wav' file, the total time is only 26:40. (13:20*3 files) should be 39.60 in length, meaning there is about 13:20 of the overall concatenated .wav file that got cut off (could be one of the audio files?)

Still new to MatLab and Concatenating, but any help would be appreciated - thanks.

P.S. I'm getting a warning when I run the task in the Command Window stating:

 >> MakeTaskfile
 Warning: Integer operands are required for colon operator when used as index 
 > In MakeTaskfile (line 17) 
 Warning: Integer operands are required for colon operator when used as index 
 > In MakeTaskfile (line 17)