1 long beep while booting

For few days now my PC has been playing an annoying beep, about 2 seconds long. But, sometimes it doesn't and plays the usual, short one. It doesn't affect the booting at all, and the PC runs mostly fine - I can do stuff no problem. Sometimes, especially when using a web browser, and not playing games, surprisingly, the whole system "stutters" for a while. I tried to find some answers in Resource Monitor, but it doesn't give me anything. I also ran memtest86, it did 9 passes but didn't report a single error. And, the system is mostly fresh, I formatted the system HDD about two months ago.

PC Specs
I also noticed my CPU overheating, in some more taxing games it goes up to 89 °C but the PC never shut down unexpectedly. I'll buy a tube of thermal paste and clean the old one when I get my next paycheck.