For as long as I can remember, one of my radiators makes a racket... I
bleed it and the noise goes away, but a few days later it comes back.

Every time I have tried to fix it (by keep bleeding it), the summer
comes and I give up.

The problem is back now and I want to fix it.. I have bleed it 3 times
this week already and again today, there is air in it?

What can I do? Where is the air coming from? Why is it always this one
radiator?

Any tips would be appreciated

All the best

Jon