Going back to garage on Monday. Fuel pump whining worse than before changed. Would have thought there would be loss of power if air getting into fuel system. Pete

Ok the fuel pump is making a high pitched whining noise. The fuel filter was changed, no difference. The fuel pump has been changed, better for about 800 miles then the whining has started up again. No noticeable loss of performance and it starts ok. Bit of a loss what to do next. Planning to...