A little late to this conversation Jim, but i had an issue a few years back now with my A4.
Had a difficult time diagnosing it.
The car would suddenly start feeling like someone had nailed a lump of wood to one of the rear tyres. Just as it get to the point of pulling over it would go away.
Finally associated it with road bumps and the suspension getting close to bottoming. That lead my mechanic mate to say "It'll be dry grease in your rear CVs".
The grease near the edges of the CV outside of normal movement will dry out over time, and that because the rear CVs never articulate a huge amount, the dry grease is near the edges. Get a decent movement of the suspension over a bump or rut and a bit of dry grease can get pulled into the CV and be a solid lump that the CV must pulverise into submission!
He was right! Cleaned and regreased all 4 rear CVs and the problem never returned.

May not be your problem, but food for thought...

The issue seemed to ga away for a while (but maybe it was that I hardly drove it in lockdown), but it’s back again! Nowhere near as violent as some of the descriptions here or in MJ’s TC thread. But it does happen at around 1800 rpm and, because it’s not too bad and only lasts a couple of seconds, no-one else seems to notice it.

But, at over 190K miles, I know that the gearbox is on borrowed time, even though it’s been to Mackies at least a half a dozen times.

Pilots have a thing called 'automatic rough', which sounds like your thing.

You get so used to the 'plane, and how it sounds that when you go over water, your senses get extra edgy, and you start to hear things and worry.

A solution is to open the window. Or give yourself a few slaps.

The issue has gone away again, but it was never as severe as some suggestions. The closest, I think, was MJ’s suggestion of the torque converter, as the slight ‘juddering’ always came on in low gear, under load and around 2K or so revs. But looking into that is way above my pay grade, so I’ll get it looked at when the problem returns.

Well, it’s still here.

My observations now are as follows:

In lower gears, at around 1500-2000 rpm, often with the engine under load (going up an incline), I get a shudder until the revs increase to above 2K.

I took it into Mackies last weekend for a ‘gearbox diagnostic’ and service. They couldn’t replicate the problem and went ahead with the service. A mile or two down the road it did it again! I sent an email to say that I wasn’t impressed, but I’m getting convinced that it’s the torque converter, so a gearbox rebuild is probably in order soon! :(

Converter clutch then. Either the friction material is worn out or the piston seal has failed so the clutch isn't locking up properly. JPAT in Bristol can refurbish the converter for about £450 iirc, although obviously getting it out is a bit of an ordeal. It might be, with labour, that its logical to get the gearbox rebuilt while its out.

Thanks Michaela. I was considering biting the bullet and taking it to Mackie's for a gearbox rebuild. They can still get the parts but they’re ‘difficult’, so the car will need to be in Glasgow for a length of time.

Best £3k I ever spent - and I expect that the longer you leave it, the more difficult it'll get...

A bit more than £3k now I’m afraid ��

MJ...
I still have a 'supercharger' noise sometimes when acceleration as the vehicle changes gear.
So what is labour time to change gearbox and torque converter?

Just thinking if I could figure out the part numbers are they still available form Audi Tradition in Germany?