When my car is idling there's a kind of a rough humming sound coming from th eengine area. Sounds like maybe a misbalanced fan or loose belt? It usually goes away once I press the gas and start moving, but it will also come back if I'm coasting without my foot on the gas. It's been doing this for several weeks now and seems to be getting more consistent.
Is this something I should worry about or should I just bring it up during my next service?
My car: 2005 S40, T5 AWD, ~50k miles