Connected pos to battery and neg to engine block. [have tried direct neg and other side of BMS too] and get a clicking sound from between the battery and firewall [fuse box] and the NOCO does not go to green and frequently goes to "bad battery error" red LED. Battery is new in August and had the same problem with the OEM - [2018 Lariat 3.5 EB] Sounds like a relay clicking in the box. Any ideas WTH is going on?
Tried the NOCO on my Honda S2000 and it worked just fine.

 

Pull the cover off the BJB [Battery Junction Box] and pull the two relays. Then try connecting the NOCO. If you can connect without a fault, then install the relays one at a time and see what happens.

If you still get the clicking and an error with the relays removed, you need to establish for sure what is clicking. A DTC scan with a diagnostic tool or FORScan might help.

 

Didn't do what you said but you got me thinking. Apparently not a common problem since you were the only reply so I scratched my head - "what is different about my truck" Totally OEM no change except I have an Ultra Gauge plugged into the OBD port.
Pulled it out and plugged in the NOCO. Heard one quieter click immediately then nothing more. Stood by for a while eventually another soft click and then no more and NOCO is now in green maintenance mode as it should be. The clicks I heard were very quite and probably would be missed if not for the history I had. Previously much more noticeable like maybe both relays were clicking and now only the one.

 

Glad you found your problem.

 

I use a NOCO Genius 5 and have a Garmin Mechanic dongle plugged into my OBD port, no issues.