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Rattling noise from under the hood

I have a 1999 Ford Escort, five speed. Until recently, I have not had any issues with it, but its age is beginning to show.

This past week, I've noticed a rattling noise from under the hood when idling, such as at a stoplight. Once I start moving, I can no longer hear the noise, though it is possible the road noise is hiding it.

Any ideas on what this is? Is it serious, or just an old car making noise?
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Comments

  • A couple of possibilities come to mind. The first should not have to be suggested, but seems to be an incredibly common problem. The first thing to check is the oil level and add if necessary. This needs to be done periodically (most owner's manuals suggest weekly or every fill-up), but very few people do it. All internal combustion engines consume some oil, some more than others. If your engine is severely low on oil, that can cause a rattling noise. If you find this condition, add oil to bring the level into the operating range on the dipstick, get into the habit of checking your oil regularly, and hope for the best.

    The other possibility that immediately comes to mind is the air conditioning compressor clutch. This can make a rattling or jingling noise when the engine is running. If turning on the air conditioning makes the noise go away, the compressor clutch is bad and needs to be replaced.
  • I would add the automatic belt tensioner to the list of things to check. Absolutely check the oil before you even start the thing again.

    If the oil level is good, just leave the hood up and start the car. If the rattle is belt/pulley related (A/C clutch; tensioner; pulley) the rattle will be on the passenger's side of the car.
  • Thanks for the comments.

    The AC compressor was actually replaced this summer. I could live without AC (I'm in WI, so surviving the three weeks of summer temperatures isn't a problem), but the clutch on the compressor was going, causing a noise when the serpentine belt went around it.

    It turns out that the problem this time is my clutch. As I understand it, there is a bearing that has shifted and makes the noise when the clutch is engaged, hence the reason I hear the noise when idling (with foot on clutch to disengage gears).
  • That type of minor detail ("clutch engaged") is immensely important. Thanks for sharing.
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