Before you go digging deep,... replace that exhaust gasket...
I think that may be all it is... without a leak up there, you will get a sharp, "
kak, kak" sound, that sounds serious...
Also, make sure your idle speed isn't too low... this ain't a Hog... it shouldn't sound lumpy.... a smooth and even purr... 900 to 1100rpm...
EDIT.. I meant..."with a leak up there"... ...