Howling Noise Around 4000 Rpm

ZXROM

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Looking for some insight on this issue. Cruising speed any gear around 4000 rpm, I started hearing a howling noise. Sounds like wind in a tunnel, very low pitched howl. Sounds like its coming from under the tank, and it will do it when free revved parked in neutral but I can really hear it when I'm wearing my helmet and moving. I just finished installing Brock's clutch mod and this was second ride after the install. I followed instructions to the t, I'm anal about everything on the bike, so I used correct thread locker where needed, main shaft nut was torqued with a snap-on torque wrench, everything was assembled properly. No power loss. no harsh noises, no idle problems or dead spots in the rpm, clutch bites hard, no slipping or chatter. The howl just started midway through the 40 minute ride. Any ideas would be appreciated. Thanks.
 
ZXROM
My first thought, taking into consideration what you mentioned, would be that something came loose/off.
It doesn't sound mechanical to me.
I'm not sure what year busa you have, but perhaps the hose that connects the air box to the block breather could be checked.
Have you had the tank up and looked at what you can see without removing anything else?
If you are familiar with your bike you might spot something out of place.

I'm happy the mod turned out well though!
 
It's a gen2 2008. I'll have to pop the tank and look at the airbox. I replaced the air filter about a 1000 miles ago, nothing looked out of order at that time.
 
Update: I narrowed down the source and it's coming from the exhaust pipes. I can hold throttle at 4k rpm and it will howl, then I can put my hand over one of the pipes and the noise goes away. Bike has voodoo stubbies on it. What would cause pipes to change sound all of a sudden? Confuesed.
 
Please don't take offense but voodoo exhaust aren't known for their outstanding quality or superior tone and sound.

Is it possible that you are just now noticing the sound because you were being more sensitive to noises after a new modification?
 
Update: I narrowed down the source and it's coming from the exhaust pipes. I can hold throttle at 4k rpm and it will howl, then I can put my hand over one of the pipes and the noise goes away. Bike has voodoo stubbies on it. What would cause pipes to change sound all of a sudden? Confuesed.

This is a great question ZXROM.

Does it matter which pipe you cover?

Can you inspect the exhaust thoroughly from the pipes to the front for any holes that may have developed. Perhaps a hole could cause a tone at a certain resonance like a tuba or some other wind instrument.

Just a thought to see where you mind is on this; If it is something that has become defective inside one or both of the voodoo stubbies, is the howl something you are willing to live with until you can replace them?

That's all I've got for now.
 
I doen't matter which pipe I cover, if I cover either one redirecting all flow through one pipe, noise stops. The howl isn't bothering me as much as the idea that something isn't right and it's not as it was before, so something must have changed. I bought my bike with these pipes, they sound petty gnarly, but hat's about it. I don't want to spend money on a different exhaust since I'll be going FI, and won't need exhaust, or at least not the conventional 2 pipe split exhaust. I'll have to inspect for other possible problems on the pipes. Noise is there all the time actually any rpm, but most noticeable at exactly 4k on decel/coast. And good point on the fact that I was more sensitive to noises since I did the clutch mod.
 
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