Northern Italy's lombard dialects carry the ö and the ü sounds: i do not think they to be of Longobard influence (they are present in Lombardy and Piedmont)but they should derive from the Gauls who settled in Italy in the third and second century, or by already existing celtic populations (e.g. the Camunians who created prehistorical engravings were Celts).
All the northern Italian towns in the Po walley have a gallic pre-roman name, with few exceptions.
Mine for example is Brixia, a gallic divinity.
Bric meant mount, if you take away the wovels you see he similarity to berg.
And Bergamo comes from the mountain god Bergimus ..

So I think the French gauls could have had such sounds themselves far before the Franks came.