[Q] Galaxy Note SHV160K issue after Jelly Bean 4.1.2

Hey guys..

I have a Galaxy Note SHV 160K [Olleh] and few days back i have updated it from Gingerbread to Jelly Bean 4.12 [official ROM].
After that i have encounterd that some times when i make calls or when im receiving calls my calls getting mute.That means i cant hear other person and he cant hear my voice on the phone.This is happening occasionally.
So, How to fix this issue?
Should i downgrade back to Gingerbread? if yes HOW?
Please Help....
Thanks in advance.