I found this thread because my system started screeching too after I installed my GTX 280.
I posted about this on the EVGA forums as well here: http://www.evga.com/forums/tm.asp?m=...55671;
I'll cut to the chase, as it turns out that in my case it's my PSU that is actually screeching and not the GTX 280.
For reference, system specs are as follows:
Q9450 @ 3.4GHz (w/ TRUE 120)
4GB (2x 2GB) G. Skill DDR1000 @ 1020MHz
EVGA GTX 280 (stock clocks)
SB X-Fi XtremeMusic
2 x 200GB WD HD (RAID 0)
1 x 300GB WD HD
PCP&C 750 Silencer
4 x Antec 120mm fans
There is actually another guy on the EVGA forums that has the same PSU as I do, and it exhibiting the same screeching noise.