We had the same issue as well a while back. Below are some instructions I got from Solarwinds support for identifying where your node/interface alerting is being duplicated.
If these are all Basic Alerts, then you could try this to see
which alerts will check for that particular device:
1) Open system manger, and open the Node Details on each of the
Nodes you need to check this against.
In the Node Details pane, note down the NODE ID of each of these
2) Open the Orion Database Manger tool, and connect to your SQL
Expand the orion database, right-click the Alerts table, and
click Query Table.
Remove the default query, and enter in the following:
Select AlertName, Enabled, NetObjects
where netobjects like '*' or netobjects like '%111,%' or
netobjects like '%222,%'
*replace the 111 and 222 with node id of your devices. The *
will pick up any alerts that are monitoring all nodes, but they will
also pick up alerts that happen to be monitoring all interfaces and all