Since you don't specify the full path of the file, matlab looks for it in the current directory (whatever that may be) or any folder specified in the matlab path. However, it can't find your file in any of these directories.
So either make sure that your wav file is in the current directory or better, give matlab the full path of the file:
rootdirectory = 'C:\somewhere\somefolder'; %obviously replace with the correct information
[x1, Fs1] = audioread(fullfile(rootdirectory, 'noisysig.wav'));
[x2, Fs2] = audioread(fullfile(rootdirectory, 'noisesamp.wav'));
