Cracking sounds and voice issue

Hi, I hope someone can help me. A have never before had issues with sound etc but this has been going on a while now and is driving me mad.
I dont know why, but all sounds are crackling and I cant use voice chat in SL or watch media. This started about 2 months ago
So....I changed to the release candidate and sounds are perfect and can use voice etc. But I would prefer to use the normal SL

Does anyone know what could be doing it?? I have removed the normal SL, cleared all the cache files from my pc as per the website and reinstalled and it is still the same.

Thanks in advance.

The RC will be the basis for the "normal" viewer in the future, right? it just includes fixes and improvements. I wouldn't worry about using it instead of the older viewer, if it works well for you.