Fs9 Sound Problem (black Screen Worst Case), New System

Hi,I did recently budget upgrade to run XP + FS9 for additional 2-3 years.My system is P5Q, E5200 dual core, Ati Radeon 4670, 2*1 gig mushkin memory, XP sp3, Avast antivirus+XP firewall.Everything is newbuilt, updated and really works like a charm.Regarding FS plan is not to install any unneeded addons to maximise stability. I use LDS, PMDG, F1 ATR, FE, GE, FSmeteo, nothing 'exotic' really.However in some cases, typically on approach 10-20 NM (several locations, could be dense clouds over Atlantic as well) out, my sound goes really crazy, becomes totally incomprehensive (just bzzzzzzzzzzz...) and takes few secs to restore. In a worst case this may result black screen without any error messages. Frame rates however remain constant. I use onboard (Realtek) sound, updated. I think it may be a confict between Ati (CCC 8.12) and onboard sound since this occurs when a lot of textures are loaded. I did lower texture_bandwidth_mult from 400 to 70 and that seems to help a bit, no CTD:s anymore. I have also tried to crash my system with Soundcheck but it remains very stable regardless what I do. Anyone able to help - I am thinking putting soundcard in to solve this, since I cannot figure out how to fix it...BR \\ Perttu