Water noise

[ian l]

I had a small water leak under my sink from the isolation valve at the top joint (hot tap). Before I had realised it was the hot tap, I turned the cold water supply off, which I turned back on once I realised what a wally I had been.
The leak is repaired, but now, when I flush the toilet, it makes an unbearable noise!!
I have a three and a half year old mega flow unvented system.

Have I created a problem by turning off the mains to it??
Can someone please offer me a solution to the noise?
Even the neighbours have mentioned the noise!!!

Thanks

[Snagbuster_Ian]

Try opening fully your stop tap