swf causing frame to scroll!

Hello all potential helpers!
I seem to have got myself into a bit of a pickle. I am using a letterbox
frameset (keeps everything centred) with a Flash nav bar loading content into
the frame below and everything works fine.... But... One section of the site
has some flash content which I have in a layer (the swf is smaller than the
page it's in) and when I preview the site something strange happens. When
navigating to the mentioned section it all seems fine but when browsing
onwards, SCROLLBARS magically appear from nowhere, both horizontal and
vertical. This problem dissapears when I take the Flash out. All scrolling is
switched off in each frame and the content is exactly the correct size.
Anybody have a clue why this is happening and maybe how to fix it?
Thanks in advance for your help.:confused;