i just got back from 40k service ,i have noticed that when i used to start up the rs there was a squelching noise, (i think some kind of injection of fuel), well its gone now and there is just a sort of click noise...any ideas please

Do you have a full tank?

You may notice it when it's down to about half.

its 2/3rds full, its always made the squelch whether its full or not though. going out in a minute so wil see if it still does the same

Should only make that noise if the fuel tank is less than half full.

BTW, what makes the squelchy noise, and what purpose does it serve?

It's the fuel pump priming the injection system.

the fuel filter is changed at the 40k service..... maybe the fuels getting through easier, so not so loud now