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Heavy mettalic rapping noise

I just bought an 07 Honda Odyssey with 34k miles. The engine is intermitently emitting a heavy metallic rapping noise. I’m wondering if it’s from the gas I put in (91 octane). The owner’s manual says if you put anything under 87 octane, such a noise might occur. Any thoughts?

The car shouldn’t “knock” on 91 octane gas. It seems your newly purchased, low mileage, 34K miles Odyssey has a potential serious problem. Heavy metallic knocking is bad, very bad.

Get this checked out immediately before something inside the motor flys apart and in effect destroys the motor.

Do you have a powertrain warranty or a dealer warranty of any kind? Including a 30-day warranty? I think you may need it.

I agree that you are foolish if you continue to operate the vehicle with a heavy metallic rapping noise coming from the engine. However, I would be interested in learning about the circumstances when you hear this noise.

Is it heard only when the engine is first started, i.e.–when the engine is cold?
Do you hear it only when accelerating?
Does it seem to be temperature-related?

And, perhaps most important of all–Have you pulled the dipstick to check the appearance and the level of the motor oil?

In any event, this vehicle needs to be examined by a competent mechanic immediately.

Regarding the noise, you need to take the car to a competent mechanic immediately to get it tracked down and corrected. Most noises like this are a very serious problem that can cause, or be caused by, serious engine problems. Regarding the fuel you are using, there is no benefit or caveat to using higher octane or “premium” fuel in this vehicle, and it will not cause this noise. Feel free to switch over to 87 octane at any time and save yourself 20 cents a gallon every fill up. By doing this, you may also have to fill up less frequently. Higher octane fuels will get you worse fuel economy, which is why you should use the lowest octane the vehicle will burn. This is one reason flex fuel vehicles get worse gas mileage when burning E85. That stuff has a very high octane rating. 105 I think? Correct me if I’m wrong.

Thanks all for your comments. I have the Odyssey in at the Honda dealer as I type this response. I am wondering, though, if my description is innacurate: I would not describe the noise as a “knock,” which some of the posters did, as much as a heavy “rrrring” noise. Unfortunately it’s intermittent, which means the dealer may not be able to reproduce the sound (it seems like they never can with these sorts of things).

Oil level is fine; and there is no pattern: sometimes it occurs within a mile of starting it; sometimes 20 miles; sometimes going down a hill; sometimes up. But always it happens when the engine is getting gas (even when downshifting while breaking).

It is covered by the powertrain warranty (for two more years) so one way or the other, it should work it’s way through–hopefully.

Continued comments are welcomed; and I’ll let you know if the dealer says anything.
Thanks again.