Question

I have my laptop hooked up to my receiver for sound output. I hear a hissing/crackling background sound that is really loud and hard to just ignore (but possible). When my 360 is connected, the sound comes out perfect, so it's just with this laptop.

Previously, I thought it was just my laptop and just submissively just let it slide. I just bought a brand new laptop though and it's doing the same thing.

I have found out more information now that I know it's not my laptop. I have used this laptop in similar environments where it worked just fine (different speakers). I have bought a new cable to connect to my receiver and it did nothing (headphone jack to RCA). I tried different ports on the receiver (Video 1-3) and it always happens.

I have discovered that the sound goes away if I unplug my laptop (so it's running on battery). Because of the last one, I tried plugging my laptop into a different outlet across the room and it's STILL doing it. Doesn't matter if I boot to Linux or Windows, yet my phone (Android G1) doesn't cause this sound using the exact same cable.

Any ideas? I'm out of them!

Thanks!

Answer 1

the sound goes away if I unplug my laptop

OK then, so if it's specifically hum that's a ground loop and you can fix it with a ground loop isolator or reduce it by playing with more earth leads.

Otherwise it's noisy DC power, which is sadly typical of poor-quality laptop power bricks (but other bad devices on the same outlet could also cause similar issues). That's not so easy to fix as it tends to involve buying proper kit like DIs, isolating transformers, ground lifts.

Either way, changing your cables for optical interconnects and/or using a better-quality external (typically USB) audio device instead of the cheapo integrated laptop audio would sort it.

Some discussion at Mefi.

Answer 2

I'm going to suggest it's a ground-loop. Essentially, the noise you're getting in the audio signal is due to a difference in the receiver's electrical ground and the laptop's electrical ground. This is why it can disappear when you're running on battery or in another location.

Try plugging it into the same outlet or powerstrip as the receiver. If you still get the audio distortion, you can try replacing the laptop's power brick, or having the laptop's power jack checked for shorts, but I'm guessing the power brick & jack aren't the problem.

To completely and properly fix the issue you may need to have your house's electrical system checked by an electrician, but that isn't a cheap fix.