Odd TentLabs/CD PRO behaviour

[evetsfrance]

Hi.
I have put together a CD player following Nico Thevissen's Phillips CD PRO based ideas which have already been discussed on this forum.
Nico is a great bloke and very helpful though his website is rather eclectic.
I'm using the TentLabs X03 clock and feeding the SPDIF output through that to a RAKK DAC.
Nico explains that a voltage divider is needed to drop the 5V tent O/P to phillips 3.3V and I found his suggestion of 220R across the ex-crystal with 100R in series to the tent clock O/P works fine. In fact I put a 500R pot across the Tent O/P and connected the crystal side to the wiper and found that a whole range of levels worked fine.
I have a really weird problem. Sometimes the Tent SPDIF O/P is fine, others it 'stutters' as if there's a bad spot on the CD. If I switch over to the Phillips analogue O/P from the on board decoder when this happens it sounds fine. Sometimes switching off for a few minutes corrects this, other times it doesn't.
Also, even when working 'properly' there are random pops (not just the end of track pop).
I'm at a loss - can anyone suggest where to look or what to do?
The power supplies to the CD PRO and XO3 are clean.