the vibrations will be minimal with these settings, u can turn down ingame strength to have even less vibration if you want and your G27 won't make those strange clunk noises
I found these to be the best G27 settings in RBR, it took me hours to tweak it to my liking, I think i tried every possible combination.
UPDATE
INGAME settings
force feedback ON
strength: max bars
direction : NORMAL
autocenter wheel: ON
Steering AXIS filter settings like curvature, saturation etc ALL OFF, rise/fall :INSTANT
Throttle filter curvature 1&2 : 6 bars rise/fall 5.0
Footbrake filter both curvatures: 0 rise/fall rate:INSTANT
Handbrake all off
clutch cuvatures: 0 , rise/fall 10
LOGITECH PROFILER settings:
overall effects strength 15% (don't like the wheel shaking vibrating too much)
spring effect strength 0% (no difference in whatever u choose i think)
damper effect strength 0% (no difference in whatever u choose i think)
enable centering spring: 60% (i like the wheel weight to be lighter for faster steering reaction)
degrees of rotation : 450
allow game to adjust settings ON
rsf launcher controls menu: gravel 150 tarmac 140 snow 115 (less means bigger vibrations)
RichardBurnsRally.ini --> ForceFeedbackSensitivityGravel=150 ForceFeedbackSensitivityTarmac=140 ForceFeedbackSensitivitySnow=115
if you don't like the clutch grabbing high at 90% try this tweak
get DXTWEAK2 open it up select your wheel, go to CLUTCH and set MIN 20 CENTER 180 MAX 255