On my review of them, I found that every couple seconds the group delay would have a spike where it would delay more than the rest, and then work it's way back, before having a spike again. As well, in the FR you would see a spike or dip in SPL when this happened as well. This was consistent with time, so if you measured it quickly, it would happen once, but if the sweep was much longer, you'd see repeating patterns of this. It's definitely something weird with the dac in it. As well, yeah the pitch seems to keep shifting