Could anyone help identify this bird please?

Hi there,

I live in the Bristol suburbs and over the last few weeks I’ve started hearing a new bird call don’t recognise.I will try and record it but until then I liken it to the stereotypical sound of a train horn when going into a tunnel. It has two medium length notes: one low and one high.  We have Goldfinch, Robins, Blue Tits and Great Tits in the area but I haven’t found anything to suggest it’s one of these, could someone help please?

Thanks, Owen