I hear a hissing noise, sort of like air leaving a punctured tire, when I am over 2000 RPMs. This is the worst when I am towing down a hill.

It started in January and my wife even noticed it, so I know it must be bad.

Anyone know what this might be? It is not the same noise I usually hear from the turbo or the transmission, it is an additional sound. I hear it behind the drivers side firewall.


Thanks,
4B

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2003 2500HD with 38000 miles. No mods.

IIRC, there have been a few posts about this same noise you describe, and it turned out to be the intercooler connections on the side of the engine. You might also check out the intake connections while you are at it.