Sometimes you will find the air trapt in a spot witch is of some distance from the bleeding point. And then sometimes it helps to stop the flow in that part of the system, that can be done by 1 stopping the pump
2 stopping [closing] the radiators in that section.
Sometimes it helps to heat up the complete system, stop it wait a couple of minutes and bleed it again.
If that all din't help, try to get as much flow as you can trough the noisy section, hopefully the trapt air takes a rollercoaster ride to the bleeder.
But how did the air became a problem in the first place?
Is the position of the vessel good? are you pumping away from the vessel?
There are so many different types of systems with different piping arrangements that a concise answer would be quite difficult to post here. You may also have a system that was never piped properly in the first place.
A call to a local heating contractor who has a "wethead" on staff would be your best bet.