An audio record of it can be listened to here:

https://d.pr/a/TklCXj

(DropLr if that is not cool I am happy to post it somewhere better)

After about 5 - 10 minutes it would start this odd phase warping.

I am sure that is the wrong term. I have not come across this before

I have changed out (all) audio cables, different speakers, various sources, different channels, different outputs. it keeps happening.

I hooked up a different mixer, same cables, sources, speakers, had it for two weeks now and it has no issues. (Its a loaner so I cant keep it)

I took it to the shop and they said they had no issues.

I take it back and I still have the issue.

I went to a PA place and harassed the guys to listen just to the recording and they had no idea either.

it is still under warranty but until I can get the shop to recreate it they wont take it.

Could it be an electrical wiring issue? It runs off an 240VAC adapter to 19V DC.