I have the following noise on my 2000 year XJ8.

click here for sound recording.

Things to note:
1. The noise is only from 1-2 and 2-3rd gears.
2. It doesn't do it 100% of the time (although more often than not).
3. It seems to happen less with a more aggressive throttle or in Sport mode.
4. The box shifts fine in all gears/reverse no clunks and no obvious slipping.

Any ideas?

 

A rather vague description, but a very common issue with the ZF 5HP is the "A" drum. Let's hope its not that. There are a number of threads on it to include a shift kit fix... https://www.ebay.com/i/373034753894?chn=ps

Barring when the last time the trans may have possibly had the fluid changed, I'd be suspect of a clogging filter and dirty fluid. If you do change the fluid, then I'd also do the shift kit since your right there.

 

The gearbox was "serviced" by which I assume oil and filter, about 10k miles ago. It's on 105k now.

 

I would, at minimum, do a fluid level check then.

 

There was once one zf 5 speed gearbox what whined on full throttle during 1-2 gears or gear shift. I cant remember. Otherwise worked like charm. It had fluid changed elsewhere. Fix was another fluid and filter change because level was about two litres low. Turned out that it was filled only engine stationary.. After oil change it has been worked since.

 

Took it to a Jaguar specialist today to drive and listen to. They said it's almost certainly just low on oil, so I'm going to put it in for a gearbox service as soon as they can do it in a couple of weeks.