DEAR CAR TALK: I have a 2004 Subaru Outback, 6-cylinder. It makes a high-pitched humming noise, like millions of crickets, after I drive at freeway speed, but only after about 10 minutes on the road.

Sometimes, it's the small car parts we think about the least that can cause the biggest problems. Take spark plugs, for example, as failing to remove seized spark plugs can threaten the engine.