I recently installed VirtualBox-5.2.0-118431 on Win10-64, and now while reproducing sound it crackles terribly. I found this problem on different PC´s (all containing Windows 2000 as VM).
I reinstalled 5.1.28-117968 and it produces no crackles, but the sound isn´t ok. neither. For example, the system sound ding.wav comes as "d-ding" - other sounds as well. I never noticed that before during reproducing music and midi files.
So, I reinstalled VirtualBox-5.1.14-112924 which I used before 5.1.28, and all works fine.
I hope the problem can be resolved soon.