Thanks for the link.  I have submitted my work order.  I hope everyone else who has this issue does also.  It is a very loud disturbing sound that I hope is nothing serious.

So - I just came home and the noise was still there.   I go down to tell Glen - he comes upstairs to hear it first-hand and now it's gone.   It's as quiet as a library in there now.

Don't know what happenned in the last 30 mins, but hopefully whatever it was it's gone for good.