First thing would be to check your transmission fluid level and condition—if it's low or dark/burnt smelling, that's your starting point. From there, a mechanic can run a proper diagnostic to see if you just need a fluid top-up or if there's something more serious going on.
I'll be completely honest here, I've owned my A4 for nearly five years now and I've been pretty diligent about regular oil changes and basic maintenance, but I just realised I've never once thought about the transmission fluid or had it checked in all that time. I was chatting with a friend who's a mechanic and he asked me when the last time was that I had the gearbox serviced, and I just stared at him blankly because it literally never crossed my mind. He gave me this look like I'd just admitted to never changing my engine oil, and said that I should really get it looked at because the transmission is one of the most expensive components to replace if it fails. I've been doing some research to figure out what I actually need to do, because I'm completely clueless about transmission maintenance and I don't even know what type of gearbox my car has, let alone what kind of fluid it takes or when it should be changed. I found a really straightforward Efficient Audi Transmission Fluid Guide Available that explained everything in simple terms, from how to check the fluid level to what the service intervals are for different transmission types. It turns out that my car has the multitronic CVT, which apparently has a pretty strict service schedule and needs a specific type of fluid that's different from the other gearboxes. I feel a bit stupid for neglecting this for so long, but I'm glad I caught it now rather than after something failed. I'm planning to book it in with a specialist next week to get the fluid changed and have the transmission inspected properly, because I'd rather spend a bit on preventative maintenance now than deal with a massive repair bill later. Has anyone else been in this situation where you realised you'd totally overlooked an important service item? I'm hoping it's not too late to get things back on track without any damage already done. Cheers.