Music which is available in the internet is not always of best quality, even if it is available in rich and fat OGG, FLAC, or WAV formats. Some people may fake the files to have higher filesharing rating, by converting them from mp3 sources. Free audio files editor Audacity can help you quickly check the track authenticity — at least indirectly.
Audacity® is free, open source software for recording and editing sounds. It is available for Mac OS X, Microsoft Windows, Linux, and other operating systems. So, open a music file in Audacity and select with a cursor a fragment with intense sound pattern, meaning not the very end and not the quietest fragments of the tune. Then go to the menu and select Analyze->Plot Spectrum. You should see something like this:
In this frequency analysis look at the right end of the graph. If the slop extends to 20 kHz — chances are you get a quality record. If the slope goes down to zero around 16 kHz (like at the example below) — the file maybe poor in quality:
Of course, if you believe (and hear) the music file sounds good, there is probably no logic in deleting it. Anyway my advice would be to get an original CD or image of it and convert the files again, if the digital copy quality is in question.