JSON result prepended with `

I am working on a project for drag and drop items in a shopping cart. For an item dropped into the cart, I am trying to implement jQuery $.ajax. The result back from the PHP is pre-pended with '`' and I can not figure out why.

This is the javascript:

$('#target').droppable({
    drop: function(event,ui) {
        var id      = $(ui.draggable).data('id');
        var aisle   = $(ui.draggable).data('aisle');
        $.ajax({
            url   : base_url+'/index.php/groceries/jquery_append_to_list',
            cache : false,
            type  : 'post',
            data  : {
                'id' : id,
                 'aisle' : aisle
            },
            success    : function(data) {
                $('#target').append('<p data-id="'+id+'" data-aisle="'+aisle+'" class="draggable">'+data.item+'</p>');
            }
        })
    }
});

This is the PHP script:

function jquery_append_to_list(){
    $id     = $this->input->post('id');
    $aisle  = $this->input->post('aisle');
    $arr    = array(
                    'r' => '1',
                   'id' => $id,
                'aisle' => $aisle,
                 'item' => 'Rye Bread');
    $data   = json_encode($arr);
    echo $data;
}

For the PHP, I am using Codeigniter as the framework. The PHP is very basic right now as I am debugging this problem so I am trying to return static response values.

The item showing up in the shopping cart is 'undefined' instead of 'Rye Bread' for the JSON array is coming into the browser as `{"r":"1","id":"7","aisle":"1","item":"Rye Bread"}.

I have stepped through the PHP with an IDE and $data is {"r":"1","id":"7","aisle":"1","item":"Rye Bread"}. Somewhere in jQuery's handling it is prepending '`' to the array.

I am using

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js"></script>
<script src="https://ajax.googleapis.com/ajax/libs/jqueryui/1.12.1/jquery-ui.min.js"></script>

as the jQuery sources. These are the same sources I use for other projects and the returns on those .ajax calls don't come back with a '`'.

The encoding in the editors used is UTF-8. The same is declared in the metadata of the browser. Thinking it might be an encoding problem I have opened the files in different editors under Windows and Linux (Linux my main environment) and nothing has shown as unexpected to account where the '`' is coming from.

For the success part I have tried

success : function(data) {
    data = data.replace(/\`/,'');
    console.log(data);
    var item = data.item;
    console.log(item);
    $('#target').append('<p data-id="'+id+'" data-aisle="'+aisle+'" class="draggable">'+item+'</p>');
}

The array data is cleaned up and variable item still comes up as undefined.

Does anyone have an idea of what to do next?