Is the motherboard BIOS latest version? Is all overclocking or XMP turned off? Even if the memory itself is rated for a specific speed, the motherboard and CPU are capable of significantly less aggressive timing. Try turning the memory speed to the lowest setting and see if the symptoms change.
Also, make sure CPU to heatsink interface is proper, as in correct amount of heatsink compound and spring tension holding the heatsink evenly against the CPU.