Eating RAM when idle

I have PC that is more than enough to cope with engine in my opinion (GTX 970, i7 4790 and 16 GB of ram) but I am having strange issues where at some moments, mostly when it is idle and when I am searching something on the internet, UE4 usage of RAM goes to 11+ and my FPS drops to 3 and it starts to freeze. When I am actively working on it, ram usage is about 4-6 GB. Is there any way I can investigate this or maybe it is know issue with 4.9?
Thank you!

Same issue with 4.10 here, 24 gigs of ram, FX 8320 and 670GTX, random ram and CPU usage when my project is open in the background and Im surfing. There has to be a fix for this.

Hello there! I can confirm that this was solved by 4.11 and there are no problems on my end when I installed 4.11. So I encourage you to install the latest preview, and then you can test if it is still persistent. They improved garbage collection a lot.