I own a 2004 S4 maual and the maintainence manual suggests replacing ribbed belt at 75000 miles. I just recently bought this car at 70000 miles and im not sure if the person before me had it replaced or not. Is their a quick way to figure out if I need a new belt? Also Im trying replace cabin filter and air filter myself. Can someone guide me as to how I can change them. Recently I noticed my car makes a heavier sound noise when its idlying but the sound disappears while driving. Has anyone experienced this problem?

Thank you for your response in advance