My phone isnt picking up the sound im hearing when my car is idling. Valve adjustment done recently. It seems to be coming from passenger side but its hard to describe. Sounds like very faint windshield wipers going back n forth fairly quick. Kind of a fluttery sound. Ive been flushing cooling system this week and yesterday was first time ive noticed the sound. Anyone know what im talking about?

 

Belt tensioner?

 

timing belt tensioner?

 

For either, analyze if the attachments meet the test for your 'faint noise at idle'.