It coule be the pump, the bearings could be worn, you'd know best as you should be able to trace the noise and determine whether it is the pump, when it starts making the noise again, place a screwdriver on the pump and put your ear on the screwdriver handle - this should tell you if it is the pump.
Changing the pump can be done by a competent DIYer, if your unsure - don't attempt it.
About £70 - £80 for a new pump. not including fitting
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