Noisy mains

[grumble]

Got a problem with noise from an ethernet-over-power set up thats causing interference on my Ashdown practice combo. Doesn't seem to affect anything else in the house or my el-cheapo 10watt practice amp. Any ideas as to a filter/conditioning solution ? The easiest would be to get rid of the adapters and run some Cat-5 but that would involve a lot of buggering about routing the cable. Maplins has a conditioner gang socket supposedly for AV filtering but its a bit OTT and costs £40, anyone tried one of these ?