Hi the first problem could be due to the pressure relief valve operating, this is a safety device that prevents overpressure within the closed loop radiator system that can cause ruptured pipes if the pressure raises to high.
The second problem could quite possibly due to the pipe work expanding and contracting with the flow of water through the system, if it is more noticeable when the heating first kicks in and after it has turned off then this is most certainly the case. Nothing you can do to stop it I am afraid, however it is a sign that your boiler is working well and pushing hot water quickly around the system.



