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Rattling in Honda Civic

We have a 2002 Honda Civic EX. Recently we have heard this rattling coming from the engine. It is the same rattling no matter what speed we are at or gear we are in. When we turn the air conditioning ON the rattling stops. What do you suppose the issue is? Thanks!

If turning on the a/c causes the noise to stop, it is most likely the air conditioning compressor clutch. The compressor clutch can usually be replaced without having to replace the entire compressor by a shop with the proper tools and know-how. Also expect some other incidentals associated with opening up the air conditioning system, such as some seals and probably a new orifice tube and receiver dryer.

I would check all the heat shields, some of which are under the hood. When a heat shield starts to come loose, it can do this. When you turn on the air conditioning two things happen, the blower motor provides “white noise” to drown out the sound, and the little engine of yours struggles, both vibrating at a different frequency, and probably also vibrating less.

We took it to a mechanic and they said it was the sound of our engine dying. Perhaps a second opinion is needed!

"We took it to a mechanic and they said it was the sound of our engine dying. Perhaps a second opinion is needed! "

You definitely need a second opinion.
This mechanic does not sound like one whom I would trust, assuming that he did not give you some basis for his “engine is dying” pronouncement.

Yes, you need a second opinion.

I think I know the sound you are experiencing, and it might not be a heat shield. It sure would be nice if you could record the sound and upload it here.

My 1998 Civic, since day one when it was new, has made a very faint rattling noise that could be mistaken for pinging, or pre-ignition, and I think that is what this mechanic thought he heard.

The Civic has never been a quiet car. Every writer who reviewed the Civic has complained about engine noise and road noise. My theory is that the noise comes from the fuel pump. It’s located under the back seats, but the foam in the back seats insulates the sound, and sound travels through solid materials better than through the air, so the source of the sound might be mistaken as though it is coming from the engine.

Like I did, you might need to just learn to live with this sound, especially if it is as faint as the sound my Civic makes.

Is your “check engine” light illuminated on your dashboard? If not, this might be a normal sound, and there’s a good chance nothing is wrong. If the CEL is on, take the car to a competent mechanic (go to a Honda dealership if you have to), and have the codes read from the computer to identify the reason the CEL is on. If it is pinging, you could have a faulty EGR valve or a faulty knock sensor.