The phrase "sneaky sources" refers to sources of information that are not easily noticed or obvious. They might be hidden or secretive, making it difficult to know where the information is coming from. Full definition
Warning: smoothies can be super sneaky sources of sugar. (prevention.com)
If you're eating less fresh food in the winter months, you're probably eating more packaged and processed foods, which can be sneaky sources of sodium. (health.com)
Beverages can be rather sneaky sources of nutritionally empty calories. (ahealthblog.com)