I too had the same problem after I installed the PS boost module & elbow. . My gauge would start to rattle at high boost readings 25-30+, however my gauge was a 0-30 type and I changed it to the 0-50. . Since the change I have no more rattle or noise??? It just may of been the brass nut and I corrected it by changing to a different gauge. Try tightening the brass nut first like CCollar advised. If that doesn't work get a new gauge!!!
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2001 HO, 6-sp, Quad Cab 4x4, 3. 54 Anti-Spin axle, Camper Special Group, 2"lift, 4" exhaust w/5" Monster Tip, BFG's tires 312x75x16's, K&N Airfilter, pod gauges, VA-CPU, PS boost module & elbow, Line X box, dimond plated tool box & rails, NorthWestern custom rocker panel with everything but leather!!!!( and maybe a warranty)!