12leavu

I've been trying to figure this out for a couple of weeks. Searched here, Google, addressed every common issue of rattles , but this one doesn't match anything I've found. This is my second z06, first one never had this issue.

2008, 20,000 miles, h/c/i car , bought it this way, everything done at vengeance racing, have all receipts. Also has full exhaust, no cats.

Here's the issue, seems worse when car is cold and sometimes is non existent. The car will not make this noise parked revving engine slowly or quickly. It only happens UNDER Light to moderate acceleration, I get a strange gurgling sound around 2-3k Rpms car is not misfiring, nor is it detecting any knock. I have hp tuners and can scan everything. The sound comes on like a vibration and goes away once I reach about 4-5k Rpms. I've included a short clip in 3rd gear and you can here the sound.



Hopefully somewhere has experienced this. It's driving me nuts.

12leavu

I found a similar post as this and it was a failed needle bearing in the stock rocker. Mine has comp trunion kit upgrade. I just went out and pulled valve covers , all looks great under there.

12leavu

I'm going to hook my wide band up tomorrow , and also log each cylinder to see if it's a misfire. I'm not sure why it would be in the midrange only, maybe to rich or lean at that range. Seems fine a wot. And the car is not jerking like an ignition misfire. Whatever the case, I will post the result. It's so easy for people to say search button, but 95% of the time people do not update posts after solved problems.

telly444

very odd

12leavu

All the plugs look good. Set my hp tuners table to view all current and misfire history. Zero misfires throughout Rpms. I'm thinking the clutch may be rattling somehow, but I can't test that by pressing the clutch, as the noise only happens while under acceleration. It will not duplicate this noise sitting still revving engine. I also put it on lift. All of the exhaust looks to have plenty of clearance with no visible rubbing areas. Also it's not as bad on the test drive I just made. When I shot that video, that is the worst it has ever done it. And sometimes it will not do it at all.

12leavu

254 views 1 reply. Lol other than me.

Why does the unexplainable always happen to me.

djfury05

Try cleaning the maf maybe? Motor mounts?

12leavu

Motor mounts are on my check list for today, I will clean maf also. Thanks

Vette @ 71

Battle flag waving in the wind??

12leavu

Cleaned maf with crc cleaner, no changes. I jacked it up , motor mounts look fine, not leaking, but I'm gonna put on my lift later today to inspect a little better.


I will also hook my wide band up at that time, but while watching hp tuners scanner , as problem occurs, all fuel trims and timing stay normal.

12leavu

Very close description!
But seriously, before I ever posted I addressed the wiper cowl, brake ducts, oil lines, inner fenders. It dose sound like a flag waving. Performance doesn't seem hindered at all, if I stay in the throttle noise goes away around 4000 rpm and pulls great to red line.

12leavu

A little more info on car if it helps. Halltech air intake, msd Air Force intake , wcch heads, kaotic cam.

Ludedude

It almost sounds like some sort of resonance in the exhaust.

12leavu

1-7/8 American racing headers/ 3" mid pipe. No cats. Stock car back.

this problem is very intermittent, I just drove the car about 5 miles and I could get it to make a noise but it was very faint nothing like on the video , same temperatures no rhyme or reason why anything should be different . Then on the way home it wouldn't make the noise at all. That's the part that makes this so hard to diagnose.

Ludedude

Yeah I hate that. Seriously though, it sounds similar to the noise I've heard on high-cube speed boats when something syncs up just right. Of course there we're dealing with multiple motors so it makes more sense.

Just my observation. My car runs stock exhaust so I can't really offer anything concrete.

Gizmo5

I have a theory, but not sure. If you're running the OEM mufflers, and its an RPM thing, maybe the butterfly flaps are going crazy.

Vac issue to flaps, fuse issue controlling it, something of them both? Just a thought, will pay attention to see how this pans out.

mewalker2

Check the exhaust actuators and vacuum lines. Do you have a mild to wild setup or have the exhaust fuse pulled? Try it with the exhaust open and see if you hear it. Could be an actuator not working right or a vacuum issue. It does sound strange but I have no other ideas. Good luck!

12leavu

I have the mild to wild switch. It makes the noise when opened or closed, the sound is definitely up front, but it possibly could be something in the rear flaps causing it to resonate up front.

I drove it yesterday several time zero noise, or very faint at times.
I drove it to work today and it's making the noise again.

I'm wondering if it could be something with the msd intake. That could explain the fact that it's not a common issue as there's not many out there installed yet.
I'm also still leaning towards a clutch rattle, because it can produce a very similar sound coming off the clutch in first gear slowly.

I'm about to the point of turning up the radio and waiting on something to break. I'm pretty sure it's not internal engine related as nothing shows on my hp tuners scan while driving it.
It definitely sounds like a rattle or air not flowing properly.
If I do give up , I will update this thread.
I've found several threads with similar issue that were never followed up. Thanks

Gizmo5

Just pop off the vac hoses to the muffler actuators to be 100% ruled out, then mark it off the list and move on to the next theory lol.

mewalker2

I know you said it sounds like it's coming from the front so do you have a Gopro you can mount on the hood or lower windshield and see if you get some better audio of it? Maybe it will help narrow down the source.