Repetitive call

Hi, can anyone help me identify what bird is making this call?

I have never seen this bird! It makes a long beeep sound, which it can repeat for hours! I first noticed late last summer, it went silent in the winter, and has just started again this week. So far it has only called for short spells of up to 10 mins.

I live.  in a small village on the edge of farmland My garden is well stocked with trees and bushes and is adjacent a large graveyard. i know we have sparrows, long tailed tits, robins, a wren, chiffchaffs, yellowhammers, chaffinch, coal tit, pigeons and greenfinches. (haven't seen blue tit in 20 years!)

A friend said it might be a Northern Bullfinch, but I haven't been able to find a recording of its song.

I know it's not much to go on, but whatever it is it is persistent.

Thanks