This study explored learners' self-generated noticing of L2 input. It is motivated by previous research on input enhancement which suggested that learners are able to notice certain aspects of input on their own without any external means to direct their attention. Drawing on insights that learner-generated noticing is largely mediated by learner-"internal" factors, this study specifically traced the effects of learners' first language (L1), and their current second language (L2) knowledge in generating noticing. Two L1 groups (Japanese and English) with no knowledge of the L2 (Korean) were exposed to written L2 input and probed for their noticing behavior under a "zero knowledge" condition, and a "some knowledge" condition (i.e., after they had been taught some L2 words). Results revealed that under the "zero knowledge" condition, both groups exhibited similar noticing patterns prompted by perceptual input properties. Under the "some knowledge" condition, however, the Japanese group seemed to have noticed more input items and processed them at a deeper level of "understanding". Insights gleaned from the study are discussed with avenues for future research.