Driving around with the boot off I can clearly hear what I felt in 4th.
When cruising in 4th, or in 4th with the clutch in, it feels like the stick is riding directly on a wobbling trans shaft.
It's worse when holding it in gear.
Not moving, in neutral, any rpm, no sound and no vibration felt.
In the video I'm holding it in every gear, just to compare. All the other gears feel fine.
At the 45 second mark in the video, you can clearly hear it, it's in 4th with the clutch in.