Transparent background isn't transparent

I am not sure if I set a pattern somewhere in Photoshop, but I have transparent backgrounds for my artboards and I exported with a transparent background, and a pattern shows up. I recognize the pattern as one I created, so I am pretty sure PS is pulling it from somewhere. 

I am using the Creative Cloud Desktop Photoshop V 24.6 and running Windows 10. 

The files are to print t-shirts, and they show up when the png is added to the design. See the attached file as an example. The file does not have a 'background' layer, only the components. I have several artboards in the same file (this is a new technique for me - maybe there is something wrong here?) I used CTRL J to create a new artboard. I copied the artwork over from a single artboard. The single artboard exported without this issue. I am editing the colour and the teal ones have a faint teal pattern and the burnt orange, a faint burnt orange.