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Hybrid passive optical networks (PONs) with a centralized light source (CLS) could be a promising solution for the next-generation PON. However, the network with a loop-back architecture will give rise to interferometric noise caused by Rayleigh backscattering (RB). Here, we propose and demonstrate a colorless optical networking unit (ONU) using a dual-parallel Mach-Zehnder modulator (DP-MZM) to mitigate RB noise in a hybrid wavelength-division-multiplexing-time-division-multiplexing PON with CLS. Both dominant contributions of RB, carrier RB and signal RB, are experimentally characterized, for the first time, when using a DP-MZM as a reflective ONU. In addition, the split-ratio of a long-reach PON using the DP-MZM-based ONU is also investigated and analyzed, showing RB noise can be efficiently reduced.