Hello everyone so I purchased a 2009 A4 Cabriolet for 4k a few weeks ago for my wife. It has high miles (166k) but was a 1 owner and looked in great shape. Since then I have already done an oil change, changed the spark plugs and replaced the coolant flange. Last week it started making this awful noise when the car is driven from 20+ minutes. No check engine lights. What could this be?