Unwanted Whoop Sound: IOS10.12.4 iCloud

Recently updated all devices to Sierra and linked all together to iCloud. On my iMac and MacBook pro, there's now a "whoop" sound that sounds off continuously on and off throughout using the device. At first it sounded like a sound generated when the laptop's lid was opened, yet it continues. Sometime several "whoops", one after another. Thought it might be caused my the pop-in alerts for email, message or reminders, but it does it when there are none. Thought maybe it was my devices taking to one another, yet when on the road with the laptop and away from other devices the laptop continues to whoop without reason and often one after another. It only does this on the MacBook Pro and iMac. Not iPhone. Not iPad. I cannot find the sound and has checked all the typical spots where sounds get assigned, yet nothing there and besides I haven't changed sounds forever. Any ideas what's causing this and more importantly how does one turn it off!

Many thanks in advance for your help on this!