Sounds like one of inductors or capacitors on the motherboard is starting to fail. If you are adventurous enough and have a steady hand with a solder iron. You can attempt to recap the motherboard if it becomes a problem.
Gigabyte Z390 AORUS-PRO Coffee Lake R 9700K, 2x8GiB of G.Skill DDR4-3600, Sapphire RX Vega 64, Corsair CX-750M V2 and Fractal Define R4 (W)
Ivy Bridge 3570K, 2x4GiB of G.Skill RIPSAW DDR3-1600, Gigabyte Z77X-UD3H, Corsair CX-750M V2, and PC-7B