Hello,
thanks for the reply, I have disconnected the silentflo 5000 from the circuit board and the noise is no longer there, once reconnected the noise returns, so it is definitely the SilentFlo 5000. I am going to try and clean it and see how that goes otherwise I think a straight replacement(probably going this way) with the Watkins E5 as I believe this is the equivalent replacement now.
thanks for your help.
Dirk