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Air rushing sound, Jake Brake

Yahoo Message Number: 98366
My coach runs fine but I have a question/concern about a noise I hear whenever I use the compression brake. I usually only can hear it when I am in a tunnel or passing close to a bridge wall or jersey barrier. It is the sound of air, a lot of air moving. Someone on the Cummins forum suggested it was a symptom of an exhaust manifold leak but when looking in that area with a flashlight, I see no evidence of soot or air leakage.

With my old coach, a rear rad DP with an exhaust brake, I know the radiator fan made a lot of noise when engine rpm's came up with application of the brake and downshifting of the transmission. I have considered the noise I hear is the side rad fan but not sure it is programmed to speed up when the Jake is activated.
Is this merely a characteristic of the 2007 and later clean diesels? Do any of you with the ISL of that year or later hear the same noise? Is it some attempt by Cummins to quiet the compression brake....perhaps due to the DPF muffler?

Gary

07 Allure 470 #31578