What is incurring Dataplex costs?

[workmaster2n]

I have a little Hello World Dataplex project where I've created a lake, added 2 zones, and added a few assets to each zone in the form of Cloud Buckets.  I've added a couple very small (10 or so items per file) json files to the assets.  I also intentionally added an illformed json file to one bucket to test what would happen.  Overall, I have maybe a few megabytes of data stored.

I've also been playing with Big Query. I've directly loaded a few 10's of thousands of rows of data (less than 100,000 rows total) directly into the BQ system either by adding JSON directly to the file storage API or manually uploading JSON files. I've run a few queries and played around with a few Looker worksheets.

The last time I played with the system I also turned on the beta features that were being advertised. I think it was Python notebooks and maybe something along the lines of versioning or something?

The last time I played with the system was on a Wednesday.  On Friday I got an alert that I had incurred one dollar worth of Dataplex charges.  I thought maybe there was a delay in some action I had done reaching the billing page.  Over the next 24 hours, I incurred an additional $3 worth of Dataplex charges.  I didn't even log into the system, so something is being automatically run to incur charges, but I cannot think of what it could be.

This is the only dataplex charge on my account.  

Any ideas how to track down what this processing is coming from?

I've disabled billing on the project so as to stop accruing charges.

Thanks!