stop Yahoo Mail notification

This issue just started, this evening.

I keep hearing an audio notification from Yahoo Mail stating: 'you've got mail'. I hear it about every 60 seconds.

No matter what I do. It won't stop.

I was using Firefox at the time... but when I logged out of Firefox and then I tried Safari and Chrome, I noticed the issue was still occurring.

I've gone into Apple, System Preferences, and clicked on Notifications...but Yahoo/Yahoo Mail, isn't listed in the box on the left, that has the scroll-down list of applications on my laptop.

I scrolled down the list and unchecked the box 'play sound for notifications' for each browser (Safari, Firefox, Chrome). That didn't work either. I still hear a 'you've got mail' message over my laptop speakers.

After I unchecked the box for 'play sound for notifications', I got out of Apple's System Preferences, logged out, and restarted my MacBook Pro. No change...I still hear the Yahoo Mail notification.

I DON'T have Thunderbird installed...which via Mozilla's (Firefox) community...was supposed to be the issue. As it's happening on whatever browser I'm logged onto tonight...it can't be Firefox related (which was the browser I was using, when the issue started, this evening).

I spoke to Yahoo via their chat window tonight...and they said the issue wasn't with them...that I had to go through the browser's menu, and stop Yahoo Mail notifications via the browser's preference settings.

Been there, done that, got the T-shirt.

I'm using a MacBook Pro (13-inch Mid 2010) laptop. It's running MacOS Mojave version 10.14.02

I haven't messed about with any System Preference settings or browser settings, prior to this issue starting, when I logged onto my laptop tonight.

I can't figure out what's initiating the message to play.

I've run out of ideas, and could use help getting this issue to stop!

Thanks