Lightpipe Crackling in one channel

I' tried using an Octopre with an ADAT lightpipe connection into my 002r unit. Everything works great for tracking except I notice that the channel one mic input on the Octopre when used as the input to a PT track has intermittent crackling sound (like static but not continuous). Maybe this is an Octopre problem or a lightpipe connector problem (I did swap out the digital optical cable and not much changed). Any thoughts? I'm new to using optical cabling so forgive the newbie-ness.. cheers M

Markus, Can you also "see" visual spikes on the meters ? This would usually indicate a sample rate mis-match. Unless the Octopre is faulty for another reason... good luck,

Make sure you have a good cable (I know you said you switched them out...it's just good to say it again). AND how is your clock set, both in pt and the octopre?