After a few minutes warming up my heating makes a lot of noise,then I hear water rushing through radiators,does this quite often during the day,could it be anything to do with my tanks in my loft,I've had system flushed also a new pump,still the same

Just to be clear, all radiators have both an inlet pipe and an outlet pipe and this is ahot water not steam system, right so far?

Your question is correct right so far

What is the purpose of tanks in the loft? How old is this installation? Is it a conversion from steam to hot water?

Does you system automatically add water if its low or do you have to manually open and close a fill valve? Your system sounds like its very low.