With everything that you have tried, as well as testing it in another machine,
there does seem to be very little left to do, that I can think of anyway. Apart
from if both machines are exact, in terms of the motherboards, I wonder if there
could be some issues with that particular card and the make and type of
motherboard that you have got in both rigs...? It does make it difficult when
you are cross testing a component in two machines when they are both built on
identical hardware to eliminate certain issues.
Do I remember rightly that some of the earlier 8x motherboards had some issues
when ran with 8x cards and the option was to force the AGP transfer to 4x for
I assume that both power supplies are also adequate for the card...? But what
you might need to consider is that the card itself could be faulty and needs to
be replaced. Have you taken it back to your retailer for at least them to check
it out for you...?
How I fixed my noisy IBM drive