fuel pump high pitch shrill

My '03 D2 TD5 74kkms started a high pitch shrill from fuel pump as it comes on when key in pos 2 and increase when engine starts.Was caught with low fuel light for 15ks then filled up,couple hours later the noise started-any connection? Anyone else had this?What to do?
Regards to all.

He who is henpecked

there is air in the fuel system, it should quieten down with time, if not then the pump is more than likely on its way out