Honda Engine Makes Rattle at 30mph

Have a Honda Accord V6 2001. Engine makes a rattle sound when you accelerate to around 30 mph, as you go faster it goes away. Most noticable when going up hill and pressing the gas, it does not make a noise when
coasting. Any ideas on what this could be?
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I have a CRV 4 cyl 2001 doing just about the same thing. It happens at 2300rpm and sounds like it is coming from beneath the car. A loud rattling at 30, and 55mph when the engine rpm is 2300. Honda dealer hears it and cannot locate the source. It's very annoying. If your mechanic finds it please let me know. Thanks Rick
On Mon, 27 Jun 2005 17:54:42 -0700, "Al Franz"

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Either loose(cracked or rusted) heat shields or a cracked A-pipe weld(IIRC,it's a double walled pipe,the inner weld,of course),the pipe from the header to the catalytic converter.Some of the heat shields can be unbolted and removed.(just don't park in tall grass;fire hazard)
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Jim Yanik
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Al Franz wrote:

Sounds exactly like knocking or pre-ignition, AKA pinging.
Simplest fix may be higher octane fuel.
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If he's using the correct octane,he may have a ignition timing problem,advanced or retarded.
Or a loose heat shield.
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Jim Yanik
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...
Yes, it could be a sympathetic vibration rattle but there are several things here that make it sound more like pinging than a vibrating part:
The noise appears "when you accelerate to 30" as opposed to "at ... mph when the engine rpm is ...".
and
"Most noticable when going up hill and pressing the gas".
I'm not sure about the 6th gen accord but I know 7th gen has a knock sensor. Supposedly, when there is pinging it detects it and the engine control system should retard the ignition (but my 2005 v6 pings under similar conditions).
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