buzz (&3 pipes at bulkhead)

[E53Steve]

Hi guys,
Nothing major but I hear little buzzing noise at tickover with a very light thud (if there is such a thing) every 1.5 -2sec approx but only hear it inside the car, when lift the bonnet I just see some pipes moving/pulsing a little to the time of the faint thud, these pipes go along the RHS of the engine and up to the bulkhead, I tried looking on realoem to see if I could find them but to no avail. Any ideas? (2008 e70 3.0d)

[Horizon]

If it were an E53 I would of. Said it sounded like the Webasco, but they didn't fit them to the E70 as standard did they, as they had a water pump that pulsed the pipes when running my 840 Ci used to have an additional small water pump that pumped water around the heater curcuit, is it the small hoses that go through the bulkhead into the heater matrix that are pulsing, can you feel water surging through them ?

[E53Steve]

correct no webasto on my e70. don't hear it all the time but have been doing some research and it looks like there may be a small water pump specifically for heating, not that expensive to replace, will monitor it and if it comes back I will get it changed.
Thanks for the info