Which kernel and Asterisk versions are recommended


Are there any recommendation in regards to which is best Kernel and which Asterisk release to run?

I am running 2.6.18-53.1.14.el5 with Asterisk 1.4.18 and I am having problems with metallic whoosshh at the background of the call that actually destroys the call quality totally. This is only one sided, meaning that called party can hear me loud and clear but calling party can’t.

I am trying to figure this out. I am running on a Dell 1650 Rack mount server hosted on the internet directly no firewalls no NAT.