Forester intermittent engine noise

Hi,

I have a 2002 Forester with the 2.5L engine. Recently it has developed an intermittent noise under the hood that can best be described like a rattlesnake rattle.

This noise only lasts 3-5 seconds, and happens during an increase to light throttle, usually around 2500 RPM, at 40-50 MPH. The sound seems to start more quietly, but then will stop abruptly. It doesn't make the sound idling, or coasting.

The character of the sound is like air whistling through an orifice, but being valved on and off quite rapidly (5-10 Hz?).

Has anyone here ever had a sound like this? What could cause it and/or how do I diagnose this further? I have not checked for engine codes yet, but there is no CEL.

Thanks, Duane

Reply to
TheSeeker
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One frequent suspect for any buzzing noise is exhaust heat shields.

Reply to
1 Lucky Texan

Heat shields. Sounds like some kid took a vacume motor, clamped a stick to it and is beating an empty metal can right? Your car is about the age where that starts. Don't remove them, just get a bunch of those band clamps (the kind with the slots on the band and the screw to tighten), poke at them (when they are cold!) and apply as necessary. My car has 6 already, and needs to go in for more. Several other Subie owners I know have had the exact same problem.

Some people say stuffing steel-wool under them works too. But I would think that would rust a lot faster than a bend clamp does.

Count on re-applying them every few years as they will fall off.

The heat sheilds do two things; 1) help prevent accidentally starting fires by parking on or driving over grass and such 2) keeps the exhaust pipe hot so the catalytic converter can work properly, if you remove them, you run the risk of your ECU going wonky or throwing errors (check engine light) due to the sensors picking up the change. It could also affect your gas milage.

In any case, take it to one of the dumbass muffler places with a bunch of the clamps and have them do it, or if you can get under it, you can do it yourself.

You could also replace all the shields, but that may get more expensive than it's worth. It's just a noise, it doesn't hurt anything.

Reply to
.._..

Hi,

Thanks for the suggestions. I have had a number of heat shields make noise, and have tracked them down. This doesn't sound at all like them, and has a different characteristic on and off pattern.

I paid more attention to it this morning on the drive to work, and it starts _always_ at 2300 RPM (no matter which gear, but must be at light throttle) and stops before the engine reaches 2500 RPM. With level or slight upgrade to the road, I can make it come and go at will, for as long as I hold it at those RPMs.

In terms of what it sounds like, it sounds like an exhaust manifold leak, but they usually make noise at all RPMs (especially at low RPMs)

Is there anything in the emission control sub-system that opens and closes, or the evaporative emissions system?

Thanks, Duane

Reply to
DuaneKaufman

Here's a link to an image with two examples of what they look like:

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On the left the silver-y formed part with the empty screw holes is one (that protects the car), and on the right the silver-y part that says "Subaru" on it with the flange with the big bolts in it (above the white filter). That is screwed on around the actual exhust pipe.

So the noise is one of these things rusting a bit and flapping when the exhaust vibrates with a certain amplitude and frequency.

You just gotta find the place and wedge something in there, use a clamp of some kind, replace the shields, or the exhaust part. It's all a matter of getting in and seeing what moves that shouldn't, look ofr corrosion.

Reply to
.._..

Any service done recently? I have read of instances where a whoosing noise is heard if the 'tabs' on the lower part of an airfilter housing do not get 'hooked' correctly.

Another possibility for a thump/knock could be timing belt rubbing due to weak tensioner. But that doesn't seam like what you describe. Can somone rev the engine for you to help pin down the location?

Reply to
1 Lucky Texan

Hi,

No Service done lately.

When the car isn't moving, the sound doesn't show up.

Thanks, Duane

Reply to
DuaneKaufman

Maybe a split CVJ boot has a 'flap' or something on it? Is there any 'jerking' or vibration? Any clicking or other problems when turning? maneuvering at low speeds? Are thires in good condition?

Reply to
1 Lucky Texan

Funny you should mention a CV boot, for as I was looking around the engine compartment for things that could be making noise, I noticed that I had indeed developed a ripped inner front passenger-side boot.

For that, I took it in to a dealer to have the axle replaced, and asked them to look into the rattling too. They said they could not reproduce it, but replaced some anchors for the foam on the lower engine cover.

No vibration no clicking when turning tires all look good

The sound seems to be tied to engine RPM like clock-work. I can get it in any gear at 2300-2500 RPM.

The sound is still there, so I think I'll have to look into it more myself.

Thanks, Duane

Reply to
DuaneKaufman

:

You may need to take a technician on a ride and create the sound for him.

Other than that - i dunno. Hope it isn't expensive!

good luck and let us know what you discover.

Carl

Reply to
1 Lucky Texan

Not to re-start this thread, but I had a noise similar to that when my head gasket blew. Maybe check the coolant level, check for bubbles in it, and inspection for coolant on the outside of the motor?

Reply to
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