Please note that issues prior to series 10 were never released on CD (pre 1990) so we can only assume these have been recorded from vinyl sources. Backup cd's for those issues may therefore have small clicks or "noise" during playback but so far we have not had any complaints. Back in the days of the US remix service "boom" FLAC or lossless methods were not well known so we can only assume that the backup cd's we have come mainly from mp3 sources (hopefully HQ ones) as their size was a lot smaller and back then storage space was very expensive on computers. Please bare this in mind when ordering - dj's and collectors trying to replace lost or damages volumes or sets should now be able to do so at a fraction of the original price.