I have one that rattles along with the pump frequency. I have swapped it from end to end - can't remember if I have done every permutation of turning it through 90degrees - currently it is horizontal.
It seems the microbore pipework is very susceptable to any shock on the leg of the radiator. Pressing the pin manually will cause a distinct shockwave.
Wondering about trying to tighten the gland nut - or removing it and packing some grease in.
Any ideas? I guess clipping the pipe bettermight help - but I ain't lifting a chipboard floor.
The locksheild is turned right down as well.