Of course, the easiest thing would be to leave the drop-arrows out like you are now.
If you want to keep them, and I can see why you would from a UI perspective, there are probably a number of ways to do it.
One thing you could do is contact the theme developer (if the jumping occurred before you modified the theme) and ask them for suggestions.
If that’s not an option, you’ll need to dig into it yourself. I recommend setting up a child theme anyway, but especially if you are going to be making more mods so they don’t get overwritten if you upgrade the theme.
If you look at line 941 of /wp-content/themes/acoustic/js/main.js, you’ll see that the code that’s adding the span tags for the drop arrow is this:
if(!jQuery.browser.opera){
jQuery("#menu ul li").each(function(){
if(jQuery(this).children('ul').length>0){
jQuery(this).find('a:first').append('<span class="drop-arrow"></span>');
}
});
}
And it is executed after the page displays when the function initSite is called on line 63 of the source of your page, so you get the jumping.
One option would be to hide the navigation menu by adding CSS to your style.css:
#menu {
display: none;
}
Then find this code, probably in the header.php file for the theme:
jQuery(document).ready(function($){
pexetoSite.initSite();
});
and change it to this:
jQuery(document).ready(function($){
pexetoSite.initSite();
jQuery('#menu').attr('display', 'inline');
});
The CSS hides the menu, and the extra line after the initSite function will display it once more after the initSite function is called and all the jumping will be done (hopefully). I haven’t been able to test this, but I’d give it a try and see if you prefer it to the jumping.