I recently bought RX-V781 AV-Receiver to replace my 11 year old RX-V757. Just as I installed it and turned it on for the first time I noticed a humming sound coming from the unit. I thoroughly checked and it’s definitely coming from RX-V781’s case, not from any other equipment that I’ve had in this setup for many years and not from any of the speaker, which are wonderfully silent with no hiss or hum. I don’t hear any hiss or hum coming from the headphones either when connected.
I’ve tried to connect the unit to different wall outlets with exact same result. The hum is fairly noticeable even during the day (with greater ambient noise) within 1,5 – 2 meters away from the unit and quite obvious at night when ambient noise is very low. I can’t hear the noise from my normal listening position though. It’s coming from the mid-left area of the case, possibly from the transformer. It’s very obvious when I hold my ear 10cm away from the case and at this range I can even detect higher pitch buzzing. I’m quite sure I can feel the area of the casing close to the transformer vibrating slightly when I lay my hand on top of the unit. I have to say that hum is slightly muffled when I touch the casing, which means the casing is resonating.
I’ve never noticed my old RX-V757 emitting any noise and it has been installed in different rooms and in different furniture. I still have it and apparently it also emits some degree of hum but in order to hear it I have to hold my ear almost against its casing and I definitely don’t hear it any further away from it. And I doubt I detect any vibration of the case.
Apart from this annoying issue the unit seems to work fine. Well, the unit also emits faint smell especially when it’s operating and warm but I attribute it to the unit being new and emitting characteristic electronics smell. My furniture is very open and I doubt it can amplify this hum. My old receiver has occupied the same spot before and I couldn’t hear it at all.
Is this hum normal or is it a sign of defect or malfunction?
