So I removed the OPPO from the mix as Wilbur and Mark suggested and hooked it directly to the XMC-1. Weird underwater sounds are now gone.
Sent an email to OPPO asking them to explain themselves . If I can't get the OPPO to work properly, I may need to move onto the Yggdrasil. Will be taking the hour drive up to the Schiitr, just north of me to check it out.
Thanks to Wilbur, Mark and DYohn for pointing me toward the OPPO being the issue. Cheers, gentlemen!
Update: The email I received from OPPO asked me to remove the UR from the chain and try the ST connected directly to the DAC. No strange sounds being made during playback this way. So it seems the OPPO and the UR don't play well together. Will wait to hear back from OPPO once again.
After listening to the UR/XMC-1 combo and the now the ST directly into the OPPO, I prefer the ST/OPPO combo with no tone controls set. I had to enable the parametric EQ in Roon to find a sound I liked with the UR/XMC-1 combo. My favorite though is the UR/OPPO combo when it wasn't make weird noises.