Bearded reedling – Panurus biarmicus
It is frequently known as the bearded tit, due to some similarities to the long-tailed tit, or the bearded parrotbill. This species is a wetland specialist, breeding colonially in large reed beds by lakes or swamps. It eats reed aphids in summer, and reed seeds in winter, its digestive system changing to cope with the very different seasonal diets.

It sounds like this
Recording by Rob van Bemmelen from Xeno Canto