Xc60 Vibration

[Loril772]

Hello all,

I purchased and collected a 2015 XC60 D4 yesterday from Peter Vardy. I usually try to avoid these big chain dealerships but the car looks to be in fantastic condition with only 39k miles and a full Volvo service history.
I Have a 90 mile round trip to work, mostly motorway so gave it a good run last night. Around town the car drives great and everything feels fine through gears 1-4 however when when I get onto the motorway and change into 5th gear I get quite a strong vibration through the gear stick and a slight vibration through the steering wheel. The vibration through the gear stick stops once changed into 6th gear but the vibration through the steering wheel remains at speeds over around 50mph regardless of road surface.
I fully intend on phoning the garage which I purchased the car from tomorrow morning but would like to be armed with a bit of knowledge as I know these chain dealerships tend to try and fob you off, especially when I'm a single female with limited car knowledge.
I'm sure they will start by telling me to try getting the wheels balanced but has anyone experienced anything like this in their xc60? I have read on another forum that some XC60s have had similar issues with 5th gear which was fixed by changing the gear selector module, could this be the issue?
Any help would be much appreciated,

Thanks.