hot water is very noisy but the heating is OK

it's a open system with a 3 way control valve, with the boiler and pump
being down stairs and the hot water tank being in the loft. It about 20
years old

my problem is that the hot water is very noisy but the heating is OK.
the noise is a whining that comes and goes and also when I first put
the hot water on there is a lot off gurgling sounds from the boiler it
all most sounds like it filing up with water, I've tried bleeding it at
the tank few times but it not helped

at first I though it was air in the system but as I've bleed it I'm now
not sure. Any help would be most wellcome

john