Weird vibrating noise from exhaust

Not sure how to describe this. On throttle application, whether in gear, or in neutral, there is a weird vibrating/pulsing bassy noise. I would liken it to a typical boxer 4 sound from a WRX. As rpms increase the vibrating speeds up. If I'm WOT right towards redline that pretty much drowns out the sound.

If you've ever heard a WRX with an aftermarket exhaust, you know what I'm talking about.

I haven't ruled out bypass valve yet, car was too hot once I got home to manually prop it open with my hand.

It almost sounds like it's something inside the muffler.

I uploaded a video of it. It helps if you have some bassy speakers so you can pick up the vibrating sound I'm talking about.

Any ideas? Thanks. And yeah, I'm going to pull the CEL, I have a feeling it's a p1448...

http://fuchi.us/IMG_0512.MOV

Youtube still processing the video, it will be here:
http://youtu.be/x6YRO8CLRk0

 

P1448 and P0157.

I also noticed hose 13 in this disagram was disconnected and dangling in the engine bay...
Ferrari F355 M5.2 (1996+) Parts : Table 8 - AIR INJECTION DEVICE

 

Bump.

I ruled out the valve by wiring it open.

 

The thing about the noise is it's not a "banging" or mechanical type of vibration. It's like constant pulsing noise in the exhaust. I'll be taking the exhaust apart today to investigate what's going on.

 

Yeah, tried that already. I pulled up on the valve and wrapped a wire around it to keep it open, still the same noise.

I'm hoping it's the top exhaust pipe with the secondary cats that is causing the issue. If the weather plays nice today, I'll be diving into it after work, and diving into a 6pack of beer.

 

Took off the mufflers today, I believe I *might* have the problem isolated, will continue work on it tomorrow. The biggest pain is taking off the bumper...

I ran the car with open cats and I think the sound went away. I also took off the bypass valve. Running open cats was obnoxiously loud and sounded like utter CRAP.

So obviously I recorded a quick sound clip
https://youtu.be/it-MDoZv7l8

 

I believe the problem is solved. While taking everything apart, the bottom two clamps on the muffler pipes were pretty loose. After putting everything back together and tightening the clamps down as much as possible (the nuts/bolts are small so I didn't want to break them) the sound is gone.

I find the whole clamping mechanisms for those two exhaust points (where the cats meet the muffler) kinda weird, there's no gasket and the nuts and bolts are small (9mm?) so it seems like they're not strong enough to stay put and might come loose in the future.

 

The saga continues...

The sound is still there, kinda. It clears up after 4000 rpms, and when in gear at speed it doesn't happen either. The weird pulsing sound happens at lower rpms and speeds under 25rpm. Sometimes it feels like there is hesitation from the throttle input and the car will kinda "hiccup" when taking off from a stop, happened at the end of my 25 minute commute today.

I'm hoping it's the clamps leaking or something, I ordered new v-clamps off ebay, they come in next week.

The piece of **** also threw a CEL at the end of my drive. I will pull it during lunch today.

I hate this bloody car. I hate it so much.

 

Holy **** I think I figured it out! The CEL was yet again a bypass valve related one.

I was inspecting everything in the engine bay in the parking lot at work trying to figure out if I missed a connection or left something unplugged.

I double-checked the air pump area to make sure there were no loose hoses that would cause the bypass valve to not open. Upon grabbing and inspecting everything it led me to the tin can in the corner near the air pump.

I felt the hoses and they were definitely on there solid. But as I tugged on them to check their connection the entire top part of the can came up. This was really odd to me because I thought it was a sealed can. I pulled up more and noticed a chunk missing from the top, and more pieces were rotting off and eventually I was pulling chunks of the top off.

So now that leads me to believe the cause of p1448 codes I've been getting ever since I've owned this ******* car.

Of course, this ****ty tin can sells for over 600 ****ing dollars on Ricambi. After some light searching you can pretty much replace it with any car vacuum canister, ~$45.

 

Well sorted: No
For sale: No
Sitting on a dealership lot to be auctioned after being traded in: Yes

 

Here are some good threads that led me to my diagnosis of the vacuum canister having a hole and not holding vacuum to open the valve:

http://www.ferrarichat.com/forum/technical-q-sponsored-algar-ferrari/329228-help-needed-f355-vacuum-tank.html

http://www.ferrarichat.com/forum/348-355-sponsored-bradan/448458-exhaust-valve-vacuum-pipe.html

"The reason that a reservoir is needed is that the bypass valve is frequently actuated at wide open throttle, when there is no vacuum to speak of. The reservoir is evacuated by the intake manifold via non return check valves and the stored vacuum used to open the exhaust bypass when needed. If everything is in good shape the tank will hold vac for days."

"However, one of the biggest issues with the bypass vacuum system on the early cars is corrosion of the vacuum reservoir. They used what looks like a big tin can, the kind that would contain Italian peeled chopped tomatoes from the supermarket. It is literally a food can.
Anyway, it rusts and leaks causing the bypass to stop working, but worse, allows unmetered and unfiltered air into the inlet manifold which can play havoc with AFR, eg. Unstable idle, hesitation and general lumpiness. "

New canister ordered from Jegs (NEVER thought I'd ever order a part from that site for a Ferrari, haha). Once the canister comes in I'll take pictures of my old one so you can see what happened to it.