pops and ticks from DAC

Bluesound Node 2i plays fine streaming and off USB drive through its own DAC and over bluetooth. Oppo-105 plays fine from FireTV, USB drive, or disc. Node 2i into the coax or optical input of the Oppo-105 produces random pops or ticks. Could happen several times in one track or not for hours.
How do each of these inputs or outputs come together? If the Node2i is the issue (still under warranty) then why only on the digital out? Wouldn't this digital signal be the same that is fed into it's internal DAC? If the Oppo is at fault then is there a common input buffer for the digital input that would effect both optical and coax but not the internal sources from the Oppo? Not knowing (or completely understanding) the internal signal geometry makes it harder to troubleshoot.
The easy thing would be to try another DAC and see what happens, but I don't have one to try. I've been thinking about upgrading my DAC but have been spending money in other areas first as the Oppo DAC is pretty good. That was one of the reasons I bought it in the first place. I don't want to waste money on a cheap DAC as a diagnostic tool. If the issue is in the Oppo S/PIDF then I guess I'll need that DAC sooner. I had been leaning toward a Chord Qutest, but that isn't in the budget this week. Would a Schiit Modi be a downgrade from the Oppo? I don't want to buy it with the intent of returning it. Maybe a Bifrost would be a lateral move or slight upgrade?
I'm not sure when it started, and sometimes I think I'm imagining it, but I've been doing more critical listening as I've been revamping the system lately. Intermittent issues are hard to diagnose. I've tried running the Oppo in pure audio mode where it shuts off all video circuitry, and that seemed to help, but I wouldn't have a clue how or why and it only occurred to me lately so I don't have much time listening in that mode. If you change something and it doesn't immediately repeat that doesn't mean it won't. All I really want to do is listen to music.
I should try that. I didn't think of alternate sources because at first I thought it was just the coax. I only use the TV fed from the Oppo. I totally forgot I can run it the other way around if I plug the FireTV directly into the TV and run optical back to the Oppo. Thanks
That’s what I can’t stand about digital - all the pops and tics!  (Sorry, I couldn’t help it) : )
Rearranged my routing last night and it sure looks like the Node2i has the issue. No response from support requests sent over the app yet. It's less than 2 months old. I went to check on Amazon to see when exactly I bought it and they had a tech help chat link. Wasted about 40 minutes with the result being that they would need to contact Bluesound. I can't imagine this is a typical problem or I would have seen something somewhere about it. I just hope it gets taken care of without too much more hassle or delay.
Finally heard from Bluesound support. I know they’re following a script, but it seems like they don’t actually read emails. Their first suggestion was to enable MQA support for external DAC even though I told them the problem occurred on local files too. I’m not even using Tidal. (Does anyone else use MQA?) There have been multiple suggestions to try a different cable. I’m no expert, but I’m pretty sure coax and toslink use different cables. Now they’ve asked me to update the firmware to the same version it already is. If they eventually make it right then I guess it will still be easier than setting up a home brew streamer and writing my own app. I’m way too lazy for that.
old thread but thought I'd put in my 2 cents.

In my experience the node 2i has trouble with very hi Rez files going out via coax to an external DAC. I get those clicks as well but only with with 192khz files. 
My streamer does this if I have both USB and SPDIF plugged in at the same time.  Different streamer (Lumin) but maybe similar causes.
I guess I never posted a resolution. There were hoops to jump through, but eventually I exchanged the Node 2i for a new one. I limited output in Qobuz to 96kHz because the Oppo input has that limit for both coax and toslink. My local files are CD quality. Never got a good answer on what the problem was, but I haven’t had the same issues with the replacement unit. Now I’m using a Qutest and have successfully streamed 192kHz files over coax and toslink. I think I just got a unit with a glitchy digital output. If it was a common problem I think their support staff wouldn’t have been so clueless and difficult to begin with. I got it resolved eventually.