It's an all in one indoor aerial. I would be tempted to buy another one but the aerial works fine when plugged into my normal tv. As I said before I wouldn't want to waste money on a new aerial for the same to happen.
But the interference could be caused BY the aerial, especially if it's a powered type as some one models are.
BT are highly unlikely to replace the box without an engineer visiting. If they do and they determine it's the aerial at fault they'll charge you a lot more than the £5-£10 a basic aerial will cost.
Anyhow, there's not really anything anyone here can do for you.
I'm lost. Why don't you disconnect the arial cable that is connected to the TV and just use the Youview box as the receiver. Why connect both?