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Hello everyone im new to this forum amd could reall use some help. Im the new ownerof a 2006 honda civic si the car ran great the first week of having it but about 2 weeks ago ot started makimg a noise that sounds like an exaust leak to me coming from under driver floor board or possible behindtje dash where the manifold would be the noise only happens once i get into 4th gear and continues threw 5th and 6th but if i push the clutch in and rev the motir while at the speeds of 55 or 60 in these gears the noise goes away also i can re create the noise while sitting at idleor with the car on jackstands amd wjeels off the ground shifting threw gears ive tried a mew exaust manifold ive tried new catalytic convortor and still the spumd is there i am mechanically inclined so if anyone has ideas please help me its driving me crazy. Thanks in advance

 
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Loud exhaust drone?
Bad engine mount?

 
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Ezone thank you for your response all help and suggestions is greatly appreciated. I'm pretty sure it's not exist drone because the sound wasn't there when I first got the car and just randomly started unless that is something that can just randomly start I will give the motor mounts a good looking over to see if there is any issues because that could be possible because here lately when I back up and go forward I get a little bit of a shake but it only happens when I back up first. To me this noise sounds just like exhaust leaks I've heard in past but only this one makes a kinda sputtering noise with it like you know how kids blow aor out between there lips and makes a sputtering noise like that so please keep suggestions coming I've looked everywhere for a leak and can't find it. Thanks

 
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Nobody else has any suggestions or have expericed something simular? Ive replace the hole exaust nothing changed i replaced motor mounts nothing changed please any suggestions is appreciated