If it is a clonking and banging noise it could be the pipes expanding and contracting as they get hot and cold. When the heating was fitted the pipes may have been installed too close together or not packed with anything between the pipes to take up the expansion. If this is the case you could consider lifting the floorboards and packing some padding (which will expand with the pipes) like some cloth etc between the pipes. A bit of a major job - it may be easier to turn the TV up!