when installing a new bt decor 1200 down stairs i moved the old bt decor 1200 to the upstairs extension, however, as soon as i plugged in the extension it caused interference on the line. i have splitters both up and down stairs,the upstairs phone is near the computer but the old phone ( philips brown plastic job ) did not create any problems like this. any help would be appreciated as mr cupid has a very low patience rating.