vga 22" display shakey with 09 white macbook

hi,
just bought a 09 white macbook to upgrade from ibook 1.42ghz

i use an iiyama 22" external display to use sibelius.

this screen was working well with the older ibook, picture was fine(used screen span doctor driver).

but when connecting monitor to new white macbook the display has a slight shimmer and shakey, its v difficult to read notation on this.

for the iiyama screen the best resolution is 1680 x1050.

when macbook is in sleep mode this resolution ( 1680 x1050 ) is automatically on the iiyama screen, but the quality is inferior to the older ibook. setting monitor at 1280 x960 stops shake but distorts the picture.

anyone know why im having this issue on a brand new macbook?
is it to do with having to use a DVI to VGA connecter on the new macbook?

any advice be much appreciated

thanks
dk

heh ,
thanks for the reply.

yeah vga is the only connection on the monitor

i was onto apple and they are to get back to me. id say your right that the signal change from dvi to vga is the cause

might have to get a new monitor

anyway thanks again