The easy solution http://www.play.com/.../-/Product.html Only 2ch basic PC sound but a total lifesaver, mine is not for sale EVER The hard solution understand and fix Is the "hum" 50Hz or 60Hz ? Make some bright picture hum and ... 1) play some genuine 50Hz out of a separate sound system, if there is a noticeable pitch difference compared to the target hum then its 60Hz* 2) Up the laptops refresh rate to 75Hz (projector may not sync) does the target hum go up further in pitch?* If NO to 1 & 2 ie "hum pitch is not video dependent" Lightly you have a regular vanilla 50Hz noise boy hum loop > not my department > skip to end. If YES to either 1 or 2 then its Video getting into audio, most lightly a combination of missing earths and a common earth perhaps in cat5, next move 3) run laptop to projector with a flexible HD15 lead removing cat5 and Kramer and converters from the game. if 1) or 2) is yes and 3) removes the problem then the escape is in the infrastructure Now bell through from the HD15 male at the laptop all the way to the projector checking earth paths, confirm how the projector straps or commons the various "earths" (explanation so far VGA / UXGA is a collection of unbalanced analogue video signals, most often at 60Hz ) In HD15 VGA/UXGA the "earths "on each of the RGB signals are separate, pins 6, 7 & 8 and then there are one or two Sync signals with separate earth conductors again, and some signaling and ID lines can you feel the standard being creatively modified as we near cat5 with less pins than HD 15 ? signal earths might be joined to save cores, then fanned out somewhere else or not or lots of other fun stuff. laptops are often double isolated with a dummy earth pin on the wall wart PSU but you have earthed it to the projector, laptops have various opinions but often strap vid earth to frame. we have a LOOP ALERT, would give you 50Hz in UK plain vanilla noise boy hum loop. Disregard if you scored YES to either 1) or 2) Suspicion now is an incomplete earth path which could cause the laptop frame to assume video signal potential 60/75 Hz keep belling, or look at Kramer and converter diagrams and finger follow the earth and signals Oh gosh the laptop frame is the audio common, unrequited video could run to earth via the sound system this way causing induction. Might be worth checking if there is one of the three primary colours causing the buzz, project pure green then pure red then pure blue, (VGA/UXGA is a Component system), if yes it narrows down where to bell. /end of long twopennyworth sorry its a load more questions *except if you need to confirm Hz in 1) & 2) a reading bass player is required,bring beer or gig oil. 50Hz (mains) is a shade above G, 60Hz (Standard VGA) is 1/4 tone under B 75Hz is 1/4 tone above D,