Yes and no. If you relax your breathing apparatus, air will escape naturally. However, if you actively hold your breath, the mounting pressure can actually lead to a tighter block. Rapidly expanding lungs are not something that falls within the daily experience of most humans, so it's best to be aware of the complications. Especially when panic sets in (and the journey upward from 30m will be quite long) it can cost a lot of self control to force yourself to exhale.