Something does not seem right. You should not get any noise from taking a high level signal and attenuating it.
I suggest that you track down the source of noise. Feed your circuit from an ordinary metal film resistor and see what types of noise you get.
In your divider, did you use the lowest resistance values that would not load down the original high level signal?
There is the possibility that your measurement system has a bandwidth that is much larger than you need. Do the calculations and limit the bandwidth as much as possible without damaging the signal you intend to measure.