HELP !! intermittant vibration in central heating system

[streekie]

hi, please help (or it could be divorce)
in this sytem there is an intermittant buzzing vibration coming from somewhere. The buzzing lasts for maybe 20 secs and occurs once every 1.5 mins. It is loud enough to wake people in the house when the central heating/hot water comes on at 5a.m.
The bathroom has a new towel rad but i have tried isolating this at the TRV and no effect. But you seem to be able to start and stop the noise with one foot either side of the bathroom door and by shifting your weight.
Where the hell do I start to sort this out ?

 

[kevplumb]

check the pipework under the floor

 

[streekie]

do you think the pipe is not secured with enough pipe clips or it is in partial contact with something under the floor.
Is this a possible air in the system somewhere thing ?
how do you explain that the noise comes and goes ?
boiler cuts in , heats water , pipe expands fractionally , boiler cuts out , pipe cools and no more contact for a couple of mins ??

 

[Nige F]

Partial contact and noise from pump. dunno why but the old pumpsets @ a large hotel where I worked used to do it...came and went.bit like me there- I came and did some work then Went and hid