Looks like Google’s plans to reinvent the way radio ads are bought has hit a rough spot. Online Media Daily reports Chad and Ryan Steelberg, the founders of dMark, an automated radio ad placement company purchased by Google in January 2006, have left the company.

The brothers resigned amid reports of growing tension between dMarc, the company they founded, and Google over differing approaches to radio ad sales. There was also said to be tension over the limited remuneration dMarc could expect under the performance-based terms of its original deal with Google.