You've been a fantastic resource as my father and I have been working on my car. Unfortunately we seem to have it a bit of a dead end on this one.
I have a 1994 manual Xantia 2.0i. I've found that above around 3k RPM there's a bit of a rattle/buzzing from the shifter, this is especially annoying when traveling at around 100km/h as I have to listen to this for 30 minute periods. The noise will stop if I push the knob slightly to the side while in gear.
My first thought was to inspect the linkage as the Haynes manual says, but honestly the directions don't seem to help much. There's no direct access to the base of the gearchange lever where it connects to the rod. There's a shield above the exhaust pipe, I didn't see any mention of this in the manual, it's also riveted in. So... we drilled out two of the rivets and had a look. It appears that even then the linkage is in a housing. I'm guessing we're doing this wrong at this point, so the project has been put on hold and I've come to ask you guys before we seriously mess things up. As far as I can tell, even if we fully removed the shield, the linkage is inaccessible due to the housing. Are we able to access it from above? If not, what's the best way of checking that linkage?
Here's a picture of just above the shield looking towards the shifter

Any help would be greatly appreciated, cheers.