Hi jonnojohnson - Welcome to Android Forums.
This sounds like an app that is installed uses Air Push Ads which would do this. You can install Ad Network Detector
from Lookout which should tell you what app is causing this. Once you remove the app the notifications should stop.
You can find other useful information regarding the Atrix in the sub forums for that phone.
Here's the forum for the Atrix 2
And here's the link for the Atrix 4G