Shimano SS Freewheels - Noise

Did you keep your old chain when swapping the cog? I've had this before when I put on a new MX30. The old one was well eaten and the chain had probably slightly stretched along with it. Stuck a new chain on - problem solved.

no bike has only done 700miles from new.. so as yet nothing swapped - PEARSON are going to send me another shimano freewheel to try which is cool of them