If either of those and it happens on the plugin’s deactivation, you can then go through and reactivate the plugins one by one until you find when it shows up again.

<script type=”text/javascript”>
amzn_assoc_ad_spec.isIframe = true;
amzn_assoc_ad_spec.linkCode = “ur1”;
window.amznBannerAd(amzn_assoc_ad_spec).init();
var amazon_assoc_ir_f_call_associates_ads = function(map) {
var logTypeStr = “”, foresterURL, json;
if(typeof JSON !== ‘undefined’) json = JSON.stringify(map);
else if(typeof amzn_assoc_utils !== ‘undefined’) json = amzn_assoc_utils.stringify(map);
else return;
if(typeof map.logType !== “undefined”) logTypeStr = “&logType=” + map.logType;
// forester URLs are of format //<end_point>/<api_version>/<channel_id>/<channel_version>/<OPERATION>/
// Depending on operation, we either pass the data in the URI or we pass them as query parameters
// if operation is OP, data must be in query parameters while if operation is TOP,
// data must be in the URI itself
foresterURL = “//fls-na.amazon-adsystem.com/1/associates-ads/1/OP/r/json”;
foresterURL = foresterURL + “?cb=” + (new Date()).getTime() + logTypeStr + “&p=” + encodeURIComponent(json);
(new Image()).src = foresterURL;
};
var amazon_assoc_ir_f_call = amazon_assoc_ir_f_call_associates_ads;
</script>

I’m not sure what you meant by checking the theme/plugins but if you didn’t deactivate as mentioned above, we can’t rule those out just yet.