F5LCI wrote:
"Maybe the feedline needs sleeves?"

When the window is closed, its "balance" may be better, or it could be
worse.

Coax could be your bon ami in eliminating the computer display noise if
used with FM/TV baluns. Ground the shield to the radio. Ferrite sleeves
around the coax may reduce transport of the interference on the exterior
of the shield to the radio.

Best regards, Richard Harrison, KB5WZI