Finding where the http request comes from

I am developing an application that use jQuery to make ajax calls to the server.

When I analyze the traffic with Fiddler I can see, as in the following picture, that I have many strange calls to an undefined URL. My code does not make those kind of calls that seems to be generated randomly.

Is there any way to discover where the call comes from? How can I troubleshoot this situation?

EDIT:

This is a sample ajax call

$.ajax({
    url: '<%= SPContext.Current.Site.Url %>' + wsBaseUrl + 'DashboardWS.asmx/MyMethod',
    type: "post",
    async: false,
    dataType: "json",
    data: JSON.stringify({ customerID: customerid, companyID: companyID }),
    contentType: "application/json; charset=utf-8",
    success: function (data) {
        result = data.d;
    }
});

EDIT 2:

Many people that has tried to help suppose that, at some time, the wsBaseUrl variable become undefined and so I can get the error showed in the screenshot. In my opinion, while this seems reasonable to me, it's not completely correct: as you can see in the sample ajax call posted, even if wsBaseUrl would be undefined at some time the resultant url shall not be /sites/shp/undefined but /sites/shp/undefined/DashboardWS.开发者_JAVA百科asmx/MyMethod. I am in fact concatenating three strings...

EDIT 3:

Following EricLaw suggestion I have tried and obtained the following result:

URL Method  Result  Type    Received    Taken   Initiator   Wait‎‎  Start‎‎ Request‎‎   Response‎‎  Cache read‎‎    Gap‎‎
/sites/shp/undefined    GET 404     0.57 KB 1.00 s  appendChild <frame> 5469    93  782 125 0   3687

but appendChild that's not in my code !!!