I had the same problem when I first installed my omori boost guage. I installed it the same location you installed it. I moved the vacume line to the line comming off the BPV and the rattle/flutter went away.
I think the root of the rattle/flutter was a disconected line under where I first hooked it up. I didnt figure this out until latter. I was also getting a CEL code once in a while. (P0457 )
Checkout this thread for details on my problem: Cel P0457
I'm not very happy with my omori guage. I eliminated the rattle/flutter at boost but now it rattles all the time when I hit bumbs in the road.