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Old 06-02-2010, 08:51 PM   #1
Hokie-wrx wagon
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Default Exhaust drone, vent holes in the trunk, and sound absorption ... need input

I have the SPT cat back exhaust installed on my '08 STI. It drones and I've been trying to come up with a game plan to fix it.

Today I had a bit of a breakthrough. I blocked both trunk vent holes with large, thick pillows. The drone was almost completely eliminated! However, I don't consider this a permanent solution. As soon as I turn on the A/C, I could feel a pressure build up in the cabin (my ears started to feel the pressure). I unblocked one vent and the pressure wasn't an issue anymore, but half the done came back.

Has anyone successfully applied sound deadening/absorbing material near the vents and still allowed them to "breathe"? Preferably something with a high heat tolerance or flame retardant.

Any input appreciated!
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Old 06-02-2010, 08:55 PM   #2
rube23
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hmmm interesting. I too would like to know since I would like to quiet down some of the in car noise from the perrin exhaust in my 08 Sti.
Maybe crack a window slightly?
where are the vent holes located?
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Old 06-02-2010, 09:02 PM   #3
ILSMKU2
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I plugged my holes (rear fenders near trunk, behind plastics and down in fender) with duct tape because my subs would rattle them on my 06 and I didnt notice any pressure build up? Nor was it any harder to shut the doors. Since those flaps are way down there, why not keep using a pillow? Its so hidden anyhow. Get a smaller one for both sides?


Hell, I have a dish towel behind my rear decks largest plastic panel because it rattled so much. Use what you can find at home and just do it!
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Old 06-02-2010, 09:30 PM   #4
Hokie-wrx wagon
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Quote:
Originally Posted by rube23 View Post
hmmm interesting. I too would like to know since I would like to quiet down some of the in car noise from the perrin exhaust in my 08 Sti.
Maybe crack a window slightly?
where are the vent holes located?
The vents are located below the cardboard floor in the trunk, on the outermost edges of the fenders.
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Old 06-02-2010, 10:04 PM   #5
Uncle Scotty
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Quote:
Originally Posted by Hokie-wrx wagon View Post
I have the SPT cat back exhaust installed on my '08 STI. It drones and I've been trying to come up with a game plan to fix it.
you have the wrong exhaust

the only real fix is to change it to one that wont resonate inside the car
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Old 06-02-2010, 10:20 PM   #6
Hokie-wrx wagon
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Quote:
Originally Posted by Uncle Scotty View Post
you have the wrong exhaust

the only real fix is to change it to one that wont resonate inside the car
Yep, that's true. However before going down the path of buying and installing another exhaust I'd like to try some simple/cheap fixes. Compared to some of the aftermarket exhausts that I've heard it's not a lot of drone to begin with, but I'm picky so I'd like to minimize it if at all possible.

I might order some of these acoustical foam wedges and give them a shot:

http://www.americanmusical.com/Item-...m_medium=feed&

The wedge shape should allow the vents to breath and may provide enough sound absorbing material to tone down the drone a bit.
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Old 06-02-2010, 10:44 PM   #7
Uncle Scotty
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Quote:
Originally Posted by Hokie-wrx wagon View Post
Yep, that's true. However before going down the path of buying and installing another exhaust I'd like to try some simple/cheap fixes.
waste of time
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Old 06-03-2010, 12:36 PM   #8
Hokie-wrx wagon
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So here's what I did to correct this ...

Per another member's suggestion, I went to HD and bought 2 square yards of their 1/2" premium carpet padding. It's fairly dense stuff. It cost $11. It doesn't smell and is flame retardant.

I used the OEM cardboard trunk floor as a template and cut the padding out 1" past the template. I put in the cardboard floor, then the carpet padding, and my OEM rubber cargo tray. Everything below the trunk floor is back to factory stock (no towels, pillows, etc). Aside from the cargo tray being 1/2" higher, you can't tell the padding is there.

From the short drive back to work, I can already tell that drone is greatly reduced! Volume is about the same, but there isn't nearly as much resonance inside the cabin.

Obviously replacing the exhaust with something that doesn't drone would be optimal. I may do that at some point in the future. For now I'll just enjoy the SPT rumble and leave the carpet padding under my cargo tray in the trunk.
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Old 06-04-2010, 05:38 AM   #9
SUBIEspecial
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if you wanna quiet the noise, dont buy an aftermarket exhaust.
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Old 06-04-2010, 07:59 AM   #10
The G.O.A.T.
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or try painting the trunk with some asphalt sealant and sand it worked for me as I have a wagon. (takes a bit to dry though but then you have a nice durable finish for your spare tire)
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Old 06-04-2010, 08:06 AM   #11
Hokie-wrx wagon
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I put more of the padding in the spare tire well.

Drone was greatly reduced at idle. It's actually only slightly louder than stock now at idle. It's also reduced throughout the rev range, but the most benefit can be heard at idle. The SPT exhaust is still a bit loud for my taste, but with the drone reduction I think I'll be able to live with it for a while longer.

Spare tire well:



With the spare tire:



On top of the cardboard floor (used the existing floor as a template):



Rubber cargo tray on top:

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Old 02-27-2013, 03:13 PM   #12
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The little thin flappy rubber piece on mine is making noise. I cut it off
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Old 02-27-2013, 06:10 PM   #13
Bryan18
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Def worth it...and a great idea. The hell with the people who said its a waste. This way you get great performance without the drone. I work at the biggest exhaust co. in the northeast and i did a set of duals on my 06 sti. I love the sound around town but on the long trips to foxwoods i wouldnt mind if its a bit quieter so ill be doing this myself this weekend!
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Old 07-10-2013, 09:02 PM   #14
WRXinpa
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Let me resurrect this old thread to say this is a very worthwhile thing to do if your exhaust's drone is killing you. I added 2 layers of 8 lb carpet padding almost identically to what is shown in the above post. I can still hear the exhaust plenty - which is good, but the brain-rattling reverberation is definitely reduced....I'd say by 40 to 60 percent, which is significant. It cost me $15 and I'm so glad I did it.

I will be looking under the back seat this weekend to see if its worth covering the bare steel there as well.
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Old 07-11-2013, 12:08 AM   #15
JasonToo
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In for someone else doing research for me.
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Old 07-11-2013, 06:36 PM   #16
Coachgids
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Anybody tried liquid deadening in the spare tire area? I'm looking at a '11 WRX hatch, and with the SPT exhaust, my wife hates it. There has to be a way to combine all the efforts expended on this subject and find a best solution. Dynamat and its variants look promising as well.
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