Are you rrunning any overclock or constant voltage? Maybe an air bubble, is the rad mounted above, beside or below the pump?
AMD 2700X, Asus ROG Strix X470-F, G.Skill Trident Z Neo 3600 (16gbx2), XFX RX 580, NZXT Kraken X62, Corsair 750D, SeaSonic 860W, OCZ RD400, Samsung 950 Pro 256Gb, Intel 520 120Gb SSD