FPS drop and sound stuttering

HI,

I've been using my AW15 R3 for half a year now, it has always been perfect. It handles game like Fallout4, NBA 2k18 and PUBG smoothly. Yesterday, out of nowhere, I started to experience FPS drop in games (i.e. 60 drop to 30 for 2K18, and 70 to 15 for PUBG)that were accompanied with sound stuttering. It happened at various frequency and seems to be more likely when there was intense sound effects.I have tried to re-install audio card and video card drivers and it didn't work. I did just installed the AW BIOS 1.2.0 BIOS update. I tried revert back to 1.1.9, it did not work. I ran Dell's online diagnostics and all my hardware seem to be functioning properly. And all video and sound played online or any where that is not in game seem to be fine. Could you please help me solve this, with this kind of FPS drop happening every several seconds I can't play any game anymore.

Thanks!!!