jQuery - why does the slide up and down has a jolt rather than being smooth?

[timmbo]

I have this code:\[code\] $(document).ready(function () { $(this).hoverAccordionMenu(); //build left menu accordion effects /*ie6 hack for mouse over icons on 2nd level. Not part of the plugin. optional!*/ if ($.browser.msie && $.browser.version.substr(0, 1) < 7) { //rollover arrow which doesn't work with simple css $('ul.menu > li > ul > li').bind("mouseenter", function (e) { $(this).css("background", "url(ico-arrow-level2.gif) no-repeat"); }); $('ul.menu > li > ul > li').bind("mouseleave", function (e) { $(this).not(".active").css("background", "none"); }); } });\[/code\]I've put in to a jsfiddle to show you:http://jsfiddle.net/haNGY/Could anyone tell me why the slide up and down has a jolt rather than being smooth?Thanks in advance!(PS, Sorry, just remembered about the title, but it's nearly 4am here so my brain is on a go slow! Just went to edit it but it's been fixed, thanks!)