Thanks both. The effect is noticeable on vla001.flac right from the start, so useful to know it plays correctly elsewhere. Curiously, the 120BPM version (2510) doesn't have this problem on my setup.

I'll do as suggested and send frozen track to PGM. It does though make me wonder about my computer - have heard that internal system interferences can cause sound oddities and that swopping sound card (Soundblaster Z SE in this case) to a different PCIe slot could make a difference, so will likely try that as well.