sound stops working after some time

[Richlv]

virtualbox 5.0.20 (same problem also appeared with 5.0.16, 5.0.18) host : macos 10.11.4 guest : opensuse 42.1

sound works just fine for a while, then it stops working. there doesn't seem to be any connection to launching applications or anything else.

attempts to reload sound modules on the linux guest side do not seem to help.

searched for existing reports, but those were either about different problems, or closed a long time ago.

VBox.log for this session is ~700k. the only messages mentioning "audio" and "sound" are from the vm startup.