The brief
The X1 had a loud noise and excessive vibration through the cabin, and on a look-over it traced to a bad engine mount, with the extra movement that caused starting to stress the gearbox mount alongside it. He brought it in. The engine and gearbox sit on rubber mounts that hold their weight and absorb the shake, keeping it out of the cabin. When one mount fails, sagged and cracked, the drivetrain moves around more than it's meant to, so the vibration comes straight through and the engine note climbs, and that extra movement loads the other mounts harder than they were designed for, so a failed engine mount drags the gearbox mount down with it. When they've gone like that you do them as a set, so they need changing together.
The diagnosis
On the lift each mount got a pry-test. The engine mount had failed, sunk and cracked, and the gearbox mount was tired alongside it, taking the extra load, the play obvious under load. All of the drivetrain mounts were past their best at the same time. When they go together like that, you do them as a set, fitting one fresh mount next to a sagging one just loads the new one harder, so the call was the full set.
The work
The engine and gearbox were taken onto transmission jacks to take their weight, and each tired mount came off in turn. New genuine BMW-spec mounts went in across the set, every fastener torqued to the manual figures. With everything bolted up, the drivetrain was checked to be sitting square in the bay before the engine was let down to load onto the fresh mounts. A road test confirmed the loud noise and the vibration were gone.
The outcome
Smooth at idle, no clatter on shifts or over bumps, no vibration through the cabin, and the engine note back to normal. The X1 went home with the drivetrain held properly again. A failed engine mount drags the gearbox mount down with it, so doing the whole set together resets the lot rather than chasing the next sagging one a few months later.
