Strange unwanted echo on input

[paulcheeba]

I've had some strange digital audio problems recently.
Firstly it was cutting out periodically at random and crackling back in so I stripped all my bnc/clocking down and put it back together. I have 4 Titans and a 16 io being clocked by a Grimm cc1 mk2. I also have an McDSP APB (which works).
I'm on a NMP 16 core with 2022.10 on Catalina.

Anyway now I have this feedback unintended echo whenever I'm on input. That sounds like a primitive digital delay. I can't find any info, everything is old and only mentions latency. I'm running hybrid and low latency.
I had this problem before but a restart normally cured it, now its permanent.

Please help?

Cheers
Paul