can you try this?
i got the feeling that it maybe an encoder/decoder issue for the difference between flac level 5 and uncompressed
in any case do a bit comparison test between the original cda in the CD and the produced flac (uncompressed) and between the flac uncompressed and the flace level 5 compressed. they all must be bit-identical to each other. when this is done use the madflac for decoder which does a bit decoding process
and then do an abx test using madflac
also check here
I used dBpoweramp to rip my CD. I ripped it in both formats and it was confirmed accurate with AccurateRip. I did an ABX test in Foobar and I could guess which was which 9/10 times. I know they are completely the same and theoretically they have to have the same sound quality. But for some reason, I hear a difference.