I have been working on some of the electrics on my 2000 XJR over the past week so I haven't driven the car at all and have noticed a leak, pretty decent appear underneath which I haven't much had too much time to investigate as of yet, stuck my finger in the fluid and didn't have a smell of trans fluid and wasn't red but I know these trannies use special spec fluid and this is probably original fluid. That is another issue however just may be connected to what I am concerned about. I got the car running again recently, wasn't doing any major work, just bulb replacement in the console.

Now when I turn the button on for sport mode, car in park, I hear a distinct noise, which I would almost describe as a bearing noise, then when I switch off sport mode it goes away so it's definitely connected. Any ideas?

I've decided to drive it directly to my shop so I can get it on a lift and inspect the leak and most likely swap transmission fluid since ill have it in the air. But wanted to see if anyone could shed some light on this or perhaps has some troubleshooting steps I should perhaps do to further diagnose the issue. Thanks so much.

Joe

 

If the leak was transmission fluid, then the gearbox fluid level may be low enough to produce the noise you're hearing.

My own 2001 XJR does the same thing when I switch between Sport & Normal modes on the gearbox, although the noise level on mine is very faint indeed. The mileage is 150k & the gearbox still works fine.

It may just be that you've lost enough gearbox fluid from the leak to make the noise louder-transmission oil cooler pipes are a favourite for corroding & springing leaks under the car.

 

There's a seal that can cause leaks where the electronics loom plugs into the gearbox.

Have a look at the connector and surrounding area, the fluid can 'wick' up the loom also and cause issues.
The gearbox connector can be unscrewed from the box and the updated seal can be replaced.
Suspect a slight underlevel if you can hear noises, usually a pump clicking, but what you're hearing might be as suggested, first gear shaft/bearing noise if it's not bathed in oil...