"Lobster" wrote
| Thanks to Owain for the suggestion about using speaker wadding;
| a good idea too although I wonder if it would it be much better
| than Rockwool (given that I already have the Rockwool and would
| have to source and buy the acoustic wadding!).

Not wadding (which is what the rockwool will do) but heavy felt panels stuck
to the pipe to reduce resonance and stop the pipe sounding like a digeridoo.
They're stuck to the inside of door panels in cars etc to dampen vibration.

Owain