I have customized the keyboard speed in the guest OS so that it fits me well. However, roughly once a minute the keyboard in the guest OS starts to work too fast, as if the settings suddenly changed to extremely short intervals. This lasts for about 7-10 seconds and then all returns back to normal. And in a minute all this repeats again and again.
I noticed that during such "fast" intervals VB eats much host CPU, though guest OS remains almost idle. Here is the screenshot of the host OS Process Explorer:

You can see these periodical bursts of activity of VB. The I/O activity (blue) are also from VB. File Monitor shows that during this period VB updates the virtual machine VDI file, but this process is not very active (here is the filtered log for one of such periods; yes, just 41 records).
The question is what to do with this? It's completely impossible to work with keyboard in the guest OS during such periods, and they repeat too often, so I can't just ignore them.