If you really want to be safe, record your own sounds - this way you know that the copyright holder has given you permission to use them. If you do not have a full copyright issue for these (or other) files or an explicit license to use them for any purpose, you may still encounter problems.
And I do not mean something like a desire:
As far as we know, blah blah blah ...
This is unlikely to delay in court :-)
The main problem with digital copies is that they are perfect reproductions, that is, the copyright owner can easily say that you thwarted their work.
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