OK, thanks for that.
Unfortunately, if the noise is within the stated parameters, then it's fit for purpose.
You can't use the distance selling regulations now as it's more than 7 days since you received it.
I'm afraid there's really nothing you can do now.
However, if you decide to fight this, it's the Co-op you have to fight.
You purchased the item from them.
Hotpoint have no contract with you (other than supplying a warranty for 1 year).
The only way you can fight this one is if the appliance is noisier than stated.
Sorry, not the news you were hoping for.
If you can get hold of a meter to measure the noise, it's worth checking to see if it actually exceeds the stated figures.
If it does, you can reject the goods as they are still noisier than stated after repair.
Check it out, it's about the only avenue left to you (unless the Co-op are willing to do something under customer relations).
Good luck with it.