Rough noise when changing into 5th over ~60mph ..?

Recently, when changing up to 5th gear, there has been a rough noise and feel from the gearstick. It only happens when going at least 60mph (silky smooth below that) and feels like clumsy clutching. Every other gear is
Any idea's what's going on?

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file
Upload is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.