You should really listen to what John is saying. Your FLAC is almost certainly truly lossless and will generate a waveform indistinguishable from the original when played back at the same levels.
If you can't be convinced this way and you really want to put your FLAC to a proper test, re-burn the FLAC-ripped track to an audio CD at the slowest speed possible, and then have a friend, spouse, or anyone someone other than you play the original and the re-rip back to back on the same player. Make sure you do not know which is playing at which time so as to remove personal bias from your judgment.
