Poor call quality since upgrading

[Tashkyzzy]

Hi I have a 640xl and I have always found the call quality brilliant, much better than my old android phone and much better than my husband's iphone. Having a hearing defect i have never struggled on my 640xl. Since upgrading to wm10 last week, the call quality is really quiet and even my 18 and 20yr old sons both agree it is really quiet (glad its not just me!). Any ideas how to improve it?