Sounds a bit like a vacuum leak and it has been inconsistent over the last several years. Often turning the inside AC/Heat to off will make it stop but not always. Also, now car has a PO108 code its throwing and I read that can happen from a vacuum leak. I cleaned up the throttle body as there was a lot of carbon. I went after this because the throttle was a bit sticky and cleaning the carbon off completely fixed that so I am happy something is better. Any ideas on the dash noise?