Currently listening to voice inversion FM comms on several of the Marine channels. It is not digital, but old style FM Voice Inversion encryption. Sounds like the same person testing on different channels.
VHF channel 25 (161.850/157.250) are VTAC 17 and VTAC 17D for some inland parts of the USA, including all of Utah.
But since you said "several of the Marine channels", it's likely someone messing around with some VHF marine radios. I know some truckers were using them for a bit (might still be).
Channel 10 and 83 are the two I remember. I'll need to listen to the recordings tonight to determine the others. There were several channels being used. It was almost like someone was testing/checking different channels. No lengthy conversations.