Embodiments of the invention include a test and measurement instrument including a test signal input and a sampler coupled to the test signal input to generate a sampled test signal. The instrument also includes a noise reduction system that includes an additional oscillator coupled to the sampler and structured to generate a sampled oscillating signal, as well as a phase detector coupled to the sampled oscillating signal for measuring noise introduced by the sampler. The noise reduction system further includes a phase corrector coupled to the phase detector for removing the measured amount of noise from the sampled test signal. Methods of noise detection are also described.