Odd noise driving me crazy. Possibly tune related? Injectors?

[2000C-5]

My specs are in my sig below. I drive my car with the top down 99% of the time, so the only time I hear this noise is when the top is up. It sounds just like valve chatter/rattle from running low octane fuel. I only run 93 octane. I have been running this build for over two years, so if something was going to fail it would have by now. I had stock LS2 heads for a while, now I have ported LSA heads. The block or heads have never been shaved/decked. Pushrods were stock at one point, they are now 7.425 Manleys. I am running a -12cc Mahle piston, so with the LS2 heads 64cc chambers I was around 10.5:1. Now with the LSA heads 68cc chambers, I am around 10.0:1. It has always had this noise and it doesn't change. It is under load in a tall gear (slight acceleration going up a hill in 5th gear or accelerating to pass on the interstate in 6th gear). I can hear my blow off valve so I can gradually increase throttle position until I hear the blow off valve close. At that point the noise stops. I used to have the stock Procharger blow off valve, now it is a Tial Q.

It seems like a long while ago, I changed something in the tune and it moved the noise to a little higher in the rpms (like the noise started at say 1500 rpm, and after it started at 2000 rpm) but, for the life of me, I don't remember what changed it. At the time I was chasing something else that was more important than the noise. I have reduced timing in the areas where it happens until the car won't hardly run, with no affect. Is there any way it could be the injectors making the noise? This could maybe explain why it quits the instant there is boost, with the increased fuel from PE and the subsequent increase in IPW (see pics). I'm at a loss. Hopefully someone has run into this before. Any help is appreciated.

no boost.JPGboost.JPG

[5FDP]

I wonder if it's just a noise coming from the exhaust. You're at a certain load, certain rpms and it just hits that right pitch where the sounds become heard more and thats what it going on.

I just want to say it's not something in the tune. The sounds you're hearing just seem exhaust related in my ears.

[2000C-5]

I thought that too, but I'm pretty sure it isn't in the exhaust. Hell, I wanted it to be in the exhaust. I tried to convince myself it was in the exhaust, but the more I listened to it I could tell it wasn't. It sounds just like valve rattle when you run cheap gas with to much timing.

[10_SS]

you dont get valve train rattle from cheap gas with to much timing, but you do get knock from cheap gas from to much timing but your logs should show lots of knock if that's what it is...

You may be hearing the exhaust pulses through the headers... that's one reason OEM's dont run real headers (thin metal), they run the heavy thick manifolds that block out allot of noise.

Or you hear drive train chatter... usually caused from changing the clutch from a spring type to a solid type, or changing a steel flywheel to a lightweight alum.

Or you have exhaust leaks at the head... I've heard this sound just like lifter ticks.

Or the blow off valve is simply rattling with all that air leaking out of it.

Or you just have general valvetrain noise... which LS have naturally.

[2000C-5]

you dont get valve train rattle from cheap gas with to much timing, but you do get knock from cheap gas from to much timing but your logs should show lots of knock if that's what it is...

I agree. I guess I was trying to explain what it sounded like. It sounds exactly like knock, but has never showed any knock with knock sensors running stock parameters.

You may be hearing the exhaust pulses through the headers... that's one reason OEM's dont run real headers (thin metal), they run the heavy thick manifolds that block out allot of noise.

I've tuned dozens of cars with headers. I've owned several cars with headers (my C5 has the same headers but isn't FI). Many friends with FI and headers. It's definitely not exhaust pulses.

Or you hear drive train chatter... usually caused from changing the clutch from a spring type to a solid type, or changing a steel flywheel to a lightweight alum.

I do have a twin disc with an aluminum flywheel and it does chatter sometimes when taking off, but this definitely isn't the noise.

Or you have exhaust leaks at the head... I've heard this sound just like lifter ticks.

No exhaust leaks. I've had two different sets of headers on it (Kooks now) and had them off and on multiple times.

Or the blow off valve is simply rattling with all that air leaking out of it.

The Tial Q by design doesn't rattle, but I had the stock bypass valve on it at one time. When I changed to LSA heads, I upped the boost and added the Tial. The noise was there before and after.

Or you just have general valvetrain noise... which LS have naturally.

Way too loud for general valvetrain noise. I have 3 vettes, one is a C5 which are the worst for valvetrain noise and it doesn't sound like this.



I appreciate your input. I hope I don't sound argumentative, it's just that I have gone through what you would call the "normal" stuff because it's been doing it for about 7000 miles now. Obviously it's not hurting anything or something would have failed by now. It just drives me nuts that I can't figure out what it is. I'm at my wits end and was hoping maybe someone had had a similar issue or maybe it was an injector or tune issue.

[10_SS]

Well, try posting a video with your phone.. I know I can get the higher frequency sounds, including knock, on an iphone video. Just dont cover the mic port.

[Montecarlodrag]

Sometimes over advanced timing makes a noise similar to valvetrain noise. It doesn't necessarily ping, it just makes noise. It's easy to fix, retard timing several degrees in the areas you hear it and it should go away.
If it doesn't, then you have another issue