Hissing noise when coasting/accelerating around 2500RPM

[JJHARRISON]

Hi guys,

I'm in need of some advice, recently purchased a 2007 outback 5sp manual and have recently noticed a hissing noise when coasting to a stop at about the 2500RPM mark, the same noise can be heard accelerating through the same RPM.
the noise stops when either the clutch is engaged, or when the brakes are applied, but i think this is because the RPM drops below that 2500RPM mark.

any help would be greatly appreciated!

***I started the car in the garage and reved it in neutral and the noise was clear at 2500RPM, although at a stand still the noise sounds slightly like a grinding/rubbng noise.

[akpv]

Probably exhaust heat shields, get under there and give them a rattle. The banana shaped ones out of the headers are commonly loose.

[Alex]

Check all the hoses, get someone to rev it up while you try and find the source.

It sounds more like a vacuum leak to me.

Sent from my HTC Velocity 4G using Tapatalk 2

[steptoe]

US counterparts talk of smoke pumped into the intake with engine stopped to find leaks. Have no idea where they get their smoke from or how they direct it in.

Is noise still there if you roll down slope at same speed engine off in neutral- AND LOTS OF VACUUM IN YOUR BRAKE BOOSTER ? so you can safely stop !!

[Brumby Kid]

A mates dad has a turbo diesel saangyong. They have a crack/ hole/ split in the exhaust turbo manifold and they lose power and it whines at a certain rpm.
To me it's gotta be air escaping from somewhere it shouldn't.

[littlewhiteute]

Hi guys,

I'm in need of some advice, recently purchased a 2007 outback 5sp manual and have recently noticed a hissing noise when coasting to a stop at about the 2500RPM mark, the same noise can be heard accelerating through the same RPM.
the noise stops when either the clutch is engaged, or when the brakes are applied, but i think this is because the RPM drops below that 2500RPM mark.

any help would be greatly appreciated!

***I started the car in the garage and reved it in neutral and the noise was clear at 2500RPM, although at a stand still the noise sounds slightly like a grinding/rubbng noise.

Clutch engaged or disengaged?

Engaged is pedal out.

[akpv]

It is something loose resonating at a certain rpm brah. Start here:

[JJHARRISON]

Probably exhaust heat shields, get under there and give them a rattle. The banana shaped ones out of the headers are commonly loose.

Thanks for the response guys!

turns out to be exactly what AKPV mentioned above, the heat shields on the exhaust. I had a mate rev the car to 2500RPM, and i was able to make the noise stop buy pressing on the shield from above with a screw-driver.

Now how to fix the problem, i tried tightening the existing bolts on the shield but they were dead-tight already. does anybody know of a solution without removing this section of the exhaust?

Thanks again!

[akpv]

Are they the hose clamps I circled?

Stainless steel hose clamp if your feeling fancy or some wire if you are feeling cheap. Other option is to get rid of the heat shields but this may reduce the life of rubber boots in the area (or on friday the 13th start a grass fire if you park in long grass)

[RSR 555]

With the engine running, get someone to try and block the rear muffler whilst you listen for leaks under the car. Also check that you have good vacuum in your brake booster.

[steptoe]

make some new shapes to it with a little hammer perhaps, thus creating some additional tension on the high pitched rattly bits .....