Sony XM5 right ear cup strange vibration noises when using noise cancelling mode

[Sam_RR]

I've had a pair of XM5s for just over a week and they've been great up until today. About 20/30 hours combined use time probably. But today I put them on and went onto noise cancelling mode and the right ear cup was giving off an odd vibration when listening to music (I checked later and it did it when not listening to anything too). It makes your ear feel blocked, gives off an odd hum and when there is loud bass it sounds like the speaker is rattling.
I checked and there is no option to update the software so I'm a bit stumped, do I return them and get a different pair or is there a fix?
Any help would be greatly appreciated! Thanks!