I’ve got a question for all those who’ve eliminated their kitty from an LLY. I recently upgraded my exhaust to a 4” system, and I’ve noticed a new noise while driving. The sound is very hard to describe but it sounds similar to when you blow air across a 2 liter coke bottle that is say ¾ full, it’s that sort of whistle noise which is new. The sound happens at approximately 1700-1800 rpm and will occasionally happen between shifts and when letting off the go pedal. You can just barely hear this noise over the normal turbo noise which I've also noticed is slightly increased with the free flowing exhaust.

<o:p> </o:p>Has anyone else with an open exhaust system (i.e. no cat converter) noticed this noise? Am I just being paranoid? This noise is definitely new since the exhaust system was installed, I also installed the Finger stick and using my Predator I can find no codes. I’m just wondering if this whistling noise is due to no back pressure to run the EGR system (I don’t have a plate installed… yet) or possibly something going wrong. I know hard to diagnose without hearing, which is why I’d appreciate any feedback from other user’s who have a similar “open” exhaust.

you may want to search for "drone". I think you may be experiencing the same as the others have been.

Interesting thought, I’d always thought the “drone” was more of a low frequency vibration type of sound vs. a higher pitched whistle… investigation commencing.

You let the cat out of the bag

Thanks for the reply Hoot. I was pretty sure that my cat going bye-bye caused it as the day after I removed the cat I began to notice this strange noise. It’s just that strange noises are not welcome on a $40 truck, I’m just glad it appears my strange new noise isn’t a strange bad new noise.

Any ideas on what causes this? You know curiosity after all *killed* the cat (damn I just had to go there) :muahaha:

My totally stock LLY has a faint, high-pitched whistle noise occasionally too at the same RPM range.

this doesn't sound like drone to me, just more turbo noise with the uncorked pipes.

the only way I can describe the drone is if you have ever been to the dentist, been under, and he is drilling. You can't feel it, but you can hear the sound in your head.

I assume what I am hearing is turbo noise. It does not do it all the time and when it does, it is not very loud. Again, mine does it and it is 100% stock.

the only way I can describe the drone is if you have ever been to the dentist, been under, and he is drilling. You can't feel it, but you can hear the sound in your head.Holy s**t now there's a noise I can live without, heck theres a description of a noise I'd have been perfectly happy not reading :lol: ya'll must be some manly men if you're driving with that noise every day.

My totally stock LLY has a faint, high-pitched whistle noise occasionally too at the same RPM range.towin43, so this faint high-pitched whistle noise you hear, it's not like a jet engine screamin right? It's more like when the wind is howling through an open window, or maybe even like a wind instrument (a flute or something) if it's anything like what I'm hearing.

I assume what I am hearing is turbo noise. It does not do it all the time and when it does, it is not very loud. Again, mine does it and it is 100% stock.One question for you, where does it seem like the noise is comming from? I'll admit I'm a bit tone deaf (shoulda listened to my Seargeants when they said use ear plugs) which may be why I never heard this noise on my stock truck, it may just be louder with an aftermarket exhaust. Anyway back to my question, to me it sounds like the noise is comming from the engine compartment, passenger side (near the EGR setup) I can duplicate the noise with the truck in park/neutral in the cab problem is when I stick my head under the hood the hurricane from the fan masks damn near all other noises. If your stock truck is making the same noise mine is (I know hard to describe/troubleshoot noises over the internet) I'd be inclined to believe this is probably just air rushing over the EGR setup, and it is simply being amplified by an open exhaust. Does this sound plausible?

Guys.. lay off the drugs! J/k...

Maybe you're right about the coke can example.. maybe its some sensor causing the noise? Like the O2.. MAF? soemthing like that perhaps?
Obviously your airflow characteristics are different now.. and since the turbulence is different.. you're hearing the air going over some intrusion that it didnt flow over before the mod.

MY .02 FWIW. I had a high pitched whistle on my mostly stock '05, but it was only present during cold starts at cruising speeds. It went away once the engine warmed. I recently tightened all the spring type clamps on the blue hoses and haven't heard it since. Although, the weather has not been as cold in these parts lately.