grabster av400 video capture problem

[mike20021969]

i used this device to capture video from my freeview box (UK) to my laptop.
all the mpeg encoding is done in the grabster unit itself and not by the laptop.

you can monitor the audio/video before and during capturing.and it all looks perfect.
however,just recently,when the mpg file is watched on window media player or real player,right at the bottom there is a vibrating white lines of a few pixels high (looks similar to telextext signal you get at the top of the tv screen in the uk).
it's never been there before-it's only just started happening.
i've tried a ads tech dvdxpressdx2 capture device this shows the same problem.

if i start by recording (using grabster) the on-screen menu which has full screen blue background then continue recording whilst i play back a recorded programme,when i then stop recording and view what i've recorded,there is no white line on the recording of the menu background part but it appears on the bottom of the recording when the recorded program plays (like i said earlier the onscreen monitoring is perfect).

some has suggested it could be cc data (closed captioning,i'm presuming) but the freeview box does not support cc.
also i tried recording something from my emtec movie cube and that is showing this 'data' line too - again only on the recording not the live monitoring preview.

what could be causing this white line to be on the recording all of a sudden? i haven't altered anything.