eTec USB ADSL modem. AM radio interference

I purchased an eTec USB ADSL modem from PC World in the UK during
October 2003.. S/N 3BE145434 on modem case using USB 1.1

The box included a microfilter. When the computer is switched on
before connection to the ADSL there is no interference on the radio. As
soon as connection is made a high pitched whistle is imposed on the
radio , irrespective of which station the radio is tuned into. This
occurs wherever the radio is placed in the house and occurs with all of
our radios (5). Also swapping computers does not make a difference,


Have you any ideas on what is causing this. Apart from this annoying
side effect, all is otherwise OK.

Main junction box loft > extension lead to computer in bedroom > ADSL
filter > USB Modem and an extension lead to downstairs (hall) DECT
answerphone.

Any ideas appreciated. Thanks.
RDD