I think this is likely to need a professional repair but I might as well ask. I use a pair of Beolab 4 as my PC speakers, so connected via the 3.5mm sockets rather than Powerlink.  This morning when I switched on my PC and they came out of standby, one of the two speakers stared making a loud static interference-like noise, and it's done that ever since.  If the 3.5mm plug is connected, it makes that noise, even if I unplug the cable from my PC at the other end. To test if it was the cable rather than the speaker, I switched the two speakers around, but it was still the same speaker that made the noise, so it appears it's not the cable. I then connected the speaker via Powerlink to my B&O AV system, and the noise was the same, but only when the AV system was switched on. The audio source is still heard, but it plays far too loud (as though the volume is on 100 when it's only on 30), and the sound quality is very poor. We're having record breaking June weather here in the UK, so maybe it's the heat!?