Currently, participants who opt in to study notifications get such notifications only sometimes (sometimes there are studies upon refreshing Connect that no notifications came through about), and they're completely silent.
At least while there are so few studies on the platform (i.e., studies aren't constantly available), participants should get notifications for every study and have the option to get audio alerts with these notifications. Also, the notifications should not group together and prevent participants from seeing the details of one particular notification, which is what currently happens if the participant has at least one study notification they have yet to open.