Intake hum when running

[mcnea001]

All:

 

The intake on the subaru makes a hum when it is running.    Almost like a low honk.

 

It was doing this before I pulled it.   This car is new to me.   Any ideas or is this a subaru thing?

 

I attached a youtube video...not sure if you can catch it.

 

 

 

Thanks,

Tom

 

 

[Bushwick]

My 95' Legacy Wagon with ej22 doesn't make that noise. It sounds like something vibrating on plastic, like the air filter box or something connected to it- like the intake tube touching metal. If you grab the intake tube, does the sound change? i.e. your hand is muffling the vibration?

 

Could also be a vacuum leak on a larger hose. Do the brakes feel like the power assist is working? Have you left any of emissions stuff disconnected? EGR valve, PCV valve, etc.?

 

You are running an air filter, right? Might want to disconnect the air filter box and see if the sound goes away. It might be air going through the intake tube and resonating on an obstruction (like air filter screen hanging down and air flow "vibrating" it) or the tube might be touching the inner edge of the hole in the inner fender where that plastic tube passes through (if it's like mine). 

Edited October 5, 2015 by Bushwick

[Loyale 2.7 Turbo]

 

I agree with Bushwick, you need to do further tests to find the culprit.

 

But it sounds like Vibration of some sort... or air getting inside the Box,

 

from a place that is not intended to allow air entrance...

 

Kind Regards.

[mcnea001]

 

 

I agree with Bushwick, you need to do further tests to find the culprit.

 

But it sounds like Vibration of some sort... or air getting inside the Box,

 

from a place that is not intended to allow air entrance...

 

Kind Regards.

 

Ok...checked around.   Looked for vacuum leaks.   Checked to make sure flow was not obstructed.   Took for a drive.

 

That is when I noticed..when I hit the accelerator...it makes a deep...WHOOOP sound.   Almost sounded like the airbox was unhooked.

 

Turned out that someone has cut the bottom out of the airbox under the filter.   I am assuming this cannot help the sounds at idle.   Why?    Should I go to the junkyard and replace.

 

Tom

[Loyale 2.7 Turbo]

I'm glad that you find the Culprit, I really Love to Help   

 

Sadly, to cut the bottom from air filter Boxes, is somehow a weird "Custom" among certain persons, who believes that such added opening, will make the air entrance, "Easier" ... like installing a Cone Filter from a Cold Air Intake; but what they really do, is to get the filter element pretty dirty, faster, and make the engine, noiser; and that noise during acceleration gives the "Placebo" effect to the drivers who believes that such "modification" makes their cars to go Faster, or accelerate faster... 

 

I've read such idea long ago, on other Automotive Forums where also I am a member.

 

Kind Regards.

[Bushwick]

I've opened up air filter boxes on other cars as part of a ton of smaller upgrades. By itself, it *can* improve airflow going into the engine but you typically want a freer flowing exhaust system to go along with it. You might loose a tiny amount of torque (talking freer flowing intake AND exhaust) in the earlier revs, but you'll get a few more hp up higher. It can also improve MPG slightly. 

 

Again, this is entirely dependent on the engine, how restrictive the factory intake is, how many hp the factory tubes are parasiting hp, etc.

 

I removed the portion of the intake piping on mine that was acting like some cheap ram intake. Basically the small slit that pulls from the front and into the fender as it just appears too restrictive.

 

On my old Lincoln Mark VIII that had a 4.6L DOHC aluminum engine that was rated at 280hp at the crank. I removed the restrictive screen in the intake tube (it was a sound deadening screen to muffle intake noise), I cut a hole at the bottom end of the air filter box (this allowed a straight shot of fresh incoming air vs. having to make a 90 degree bend into the box), installed freer flowing Summit Racing Turbo mufflers (the quiet ones), ran full synthetic oils from engine to trans to rear end, custom lowered the brackets for the air bag suspension to allow a 1.5" drop front/rear, ran touring tires, ran a K&N air filter, fresh plugs and wires (spark plug strap was custom filed back to sit a little less than dead center with an angled bevel- this reduces hesitation, frees up around 5hp to V8's, and was an old drag racing trick from the 60's - 70's). The car had a real-time MPG monitor which was surprisingly accurate. From the factory, these cars got 28 mpg highway (awesome feat considering the car weighed 3800 pounds and had a larger V8 + a 4 speed auto, although it did have a 3.08 final gear) and I think 18 city. After doing ALL the aforementioned mods, highway MPG with cruise set on flat highway (doing 70 MPH) it's got 33 MPG. City was 20-22 if you kept the gas pedal sane. AVG MPG was typically around 25, assuming there was a decent amount of highway usage. This car was long and low, and seems like a decently low coefficient drag, which when combined with everything else, made these numbers possible. I did a ton of highway driving with it and those numbers backed up what was going in the tank. 

 

So, does the air intake hole by itself help with much? No. Although, when engineers are more worried about keeping engine noises to a minimum so little old ladies don't gripe about their family hauler making excess noises, it can actually impact performance if they put a ton of bends into the intake piping and restrict diameter of piping at any places. Those bends and restrictions are primarily done for the sole benefit of noise suppression above all else.

 

If it were me, I'd's just remove as much of the box as possible w/o disturbing structural anchor points (all opening must be AFTER the filter so it can still do it's job). That'll remove that humming effect which sounds like air is whistling across the hole they added. If you widen the hole or remove the bottom of the box with say a dremel, it'll act similar to a filter on a tube. Your intake will sound a little more throaty when you step on it, but that whistling should go away.

 

As far as a dirtier air filter, it shouldn't matter unless your engine compartment is filthy. Most engine air is from the engine compartment anyways. For best performance and MPG, you should be changing your filter yearly anyways. More so if you drive in really dirty areas like the desert or have a long gravel driveway, etc. 

Edited October 6, 2015 by Bushwick