Advice on my ride-on please.......
 

Hello,
I bought a new Toro XLS 420T, and all was ok to start with, but soon the gearbox started making a lot of noise when the lever was pulled out so i could push it.
The dealer came out, took it away, and said they put a new gearbox into it. When i got it back i tried it and the back wheels locked up, but it works ok when the engine is running so i used it a little, and now the gearbox when i'm pushing it is more noisy than it was before they fixed it.
Their stance now is that they just think that's what this gearbox does and it's under warranty so don't worry.
All sounds very vague and disconcerting to me, and the mower is only 4 months old.

Has any of you experienced something like this before, or have any advice or tips?