A different jake problem

some trucks have been programmed that when the jake is fully engaged it also engages the fan hub, so there is even more drag on the engine to slow you down.

 

What year and engine? If its like my Detroit the way I understand when the jakes come on the turbo puts back pressure on the engine as well. If you have a gasket leaking on your manifold that could be causing the noise. I've seen that happen on a Dodge with the 6.7 cummins; actually a fairly common problem. Its very annoying though. Hope you can find a solution.

 

You likely have an exhaust leak. Its either between the EPG housing and turbo, or turbo and manifold, or lastly manifold and head. Most of the ones we have worked on it was leaking between the turbo and manifold.