My diff doesn’t leak (PO has done seals & bearings etc) but starts to gently whine at 50mph on moderate throttle - either back off or hit the pedal and it stops.
It sounds like a bad alignment of pinion and crownwheel might be the cause but, in any case, I’m not sure how much of a worry this is.
G’Day Stuart.
The diff (3.5) in my elan does the same… but it has done a big mileage, if a diff has been reco’d the preload setting may be the cause. But the 3.9 diff I sometimes use is very quiet at all times.
Several decades ago I had a triumph from new and the diff had a bad period whine at 100KPH… it was stripped and reset three times in the workshop… it made no difference, simply gave up on it in the end.
I just went through the same experience. I posted it.
New Drive shafts
New top diff mounts
New bottom mounts
In the end a fresh Diff’ rebuilt by an expert
Red line oil.
Ran it in etc.l
I have virtually go rid but there is still a little whine as you say when not under heavy load or not coasting. I would live with It. Must have put ?650 into this. By the time I got the newer diff’, the old one (that had been rebuilt) was starting to become more quiet.
If everything is sound in the area and you have no vibration, I would run it. You could try some Red Line diff’ oil as Rohan suggested.
Regards Mike
PS Sorry, could not resist, what is it singing? Elvis