The rattling noise started to happen about a week ago. You can clearly hear it once the car accelerates. It's not a constant noise but it occurs every now and then when driving. I brought it in for the mechanic to check it out and said it's nothing to worry about. Said the car is perfectly fine and the only problem is the annoying noise it'll make. Is this true?

 

What year/model accord do you have?

If the heat shield has a fine crack near the bolts, then the rattling sound will just annoy you. You can replace the heat shields if you like.

 

Do not rip the heat shield off as it also protects the converter from damage from road debris.

 

It's 2000/Accord LX. If it is the heat shields, how much does this typically cost to get fixed?

 

The heat shield (#5 & 6) is fastened around the converter (#2) under the car. IF that's what's rattling, it's common for it to be cracked around the mounting bolts. You can do something low-tech like hose clamps around the front & back to clamp it back into place.


But sometimes the rattling comes from the actual exhaust pipes being cracked.

 

It's not the heat shield after all. Took it to another mechanic and also said the problem was coming inside the converter. He told me not to worry about it. Said the only issue it'll have is the rattling noise. I can deal with the noise as I was told it's quite expensive to replace this part but I just don't want a misdiagnosed that can lead to something else more serious damage in the future.

 

Listen for changes in the sound over time. The ceramic guts of the cat must be cracked or something. As the broken pieces rattle against each other, it's bound to get worse. Maybe one day (or maybe 10 years from now) the broken pieces might shift position & make a big obstruction to the flow of exhaust.

This is not to make you panic & buy a new converter; but just be aware of that if you ever notice loss of power. When internet boards hear about loss of power, a broken converter isn't the first thing to come to mind.