Thanks for your reply. After digging around I think I've found the solution. The slow hangs happen on the VMs where I use bridged networking. I'm using that on virtualbox rather than the default NAT as I need each virtual machine to have its own unique IP for accessing the outside world through my physical wireless card whenever more than one VM is running simultaneously. They then use a second "Host Only" virtual adapter for accessing the local host LAN for internal communications. This is all set up for using Kali and Metasploitable for security testing. I'm not sure why, but a solution (other than using NAT) is to disable IPv6 on the bridged hosts by editing /etc/sysctl.conf and restarting network services. I still need to explore why this is an issue with bridged networks for virtualbox. Here is the link where I found this:
http://www.techrepublic.com/article/how ... -machines/Anyway, just f.y.i., and thanks again for your input.