Thanks ita basically a new system fitted a few months ago with cheap valves so may not need flushing just the valves changing thanks for your advice
Well, no...
It is no shock to find that this system has just been installed. The industry is a mess so i wouldn't automatically assume it has been installed correctly.
New valves won't reduce the flow rate causing the noise.....
Go and have a look at the pump. Is it set to max speed?
How many rads do you have? Have they had the lockshield valves set?
A suggestion is to go round the rads to the lockshield valves and close them, taking note of how EXACTLY many turns each take,
If the valves are all fully open, then the system has not been balanced at all.
Or, if it's been just shoved in, you may find the valves are all nearly closed and making the flowrates in other parts bad.
A common trick where lockshield valves are in a mess is is to set all of the lockshield valves to 1/2 turn, this should be a decent average for the system (the valves are sensitive on the fisrt turn or not).
So, once armed with what the valves are set at now, set them to the 1/2 turn trick and see how you get on. you can always revert back to the settings they were at if you think they were done correctly (I doubt it).
If you know the rads are all fed from a manifold, then just open the lockshield valves fully.
The above is what i would do, but i am not a plumber.
Go around and reset the lockshields to 1/2 turn. Make sure the pump speed is on 1 and see how it works out.
If the system don't like speed 1, try speed 2.
If the rads are heating unevenly, trim lockshields to suit.
Best of luck. I am sure a plumber will be along to give you a correct answer but i feel you shouldn't be rushing to the system with the spanners just yet.