You can double check for triggers with:
use YourDb select * from sys.objects where type = 'TR'
EDIT: this is like an ASP.NET membership that ends in a user database (this is not a SQL Server login). Can you see which connection string the ASP.NET membership provider uses? This is usually in Web.config, for example:
<providers> <add name="AspNetSqlMembershipProvider" ... connectionStringName="<<connection string>>"
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