A metallic rattling noise suddenly started on my 1999 Land Rover Discovery TD5.  It was not very loud and could only really be heard with the engine idling.  It was also accompanied by a clung when the engine was turned off.  I traced the noise to the inside of the bell housing.  If I covered the vent hole at the bottom of the bell housing (the U shaped hole in the photo), the rattling sound was muffled.  After doing some research on the internet, I was convinced that the ‘Flexplate’ that couples the torque convertor to the crank shaft must be cracked and about to fail.  Replacing the flexplate would require the gearbox separating from the engine, a job I was not looking forward to doing.  I priced up a new flex plate from a Land Rover dealer, which was only £18, but no doubt getting them to fit it would be a several hundred pound job.

The first thing to do was verify that the flexplate was indeed at fault, so I raised the vehicle and removed the circular plate from the bottom of the bell housing so that I could inspect the flexplate.

The photos above, taken through the hole in the bottom of the bell housing show that the flexplate is not faulty at all.  I turned the engine over to check the far side of the flexplate, again with no cracks.  The only other thing in the bell housing that I could imagine making the rattling noise was the starter motor, so I decided to remove it to check it out.

The started motor in situ.

The power cable disconnected.  I had already disconnected the battery.

The ring gear that the started motor drives.  Everything looked OK in there.

The rattling turned out to be that the starter motor pinion was not returning fully as can be seen in the left photo, compared to a spare starter motor that I had in the right photo.

Before fitting the spare starter, I thought I would check the solenoid contacts to make sure they were OK.  I had previously replaced them in the original starter.

The solenoid contacts were a little worn, but were still serviceable.

The fault on my original starter turned out to be that the spring on the solenoid had snapped and had jammed, causing the pinion to not fully return home.  I was also surprised to find that the new contacts that I had fitted a couple of years ago were almost worn away.  Anyway, fitting the spare starter solved the rattling noise.