Macbook display port causing noise on firewire interface

[James B]

Have any of you heard of this before?

I'm using an Alesis io26 firewire interface with a 2009 Macbook Pro and whenever my external monitor is plugged in to the display port via a HDMI adapter I hear this terrible noise. The closest comparison I can think of is artifacts from a really low bit rate MP3, like an audiobook from 1997 or something. Unplugging the Macbook charger makes the noise louder/ worse. When the monitor is unplugged it's fine. My USB audio interfaces have no such problems.

I've tried it with different power outlets and with a different HDMI adapter/ cable, I've tried unplugging peripherals. No luck.

Switching my laptop for my brother's almost identical MBP solves the problem which is kinda frustrating as my laptop is 3 months out of warranty and if my previous Apple repair experiences are anything to go by this will be a logic board replacement situation.

The weird thing is that if I turn down the volume of my monitors and compensate by raising it on the interface the noise becomes quiet enough to be ignored in general use. Confusing.

I guess this is more of a moan or a curious attempt to understand what's going on here rather than a shot at actually fixing it, but maybe someone here has experienced the same thing...

[Woodeye]

Not the same thing, but something equally as odd; my mobile phone would completely drop its voice/text signal (but not it's data signal) when I got a new PC laptop (not Macbook), and hooked up my DVI display with a DisplayPort-DVI cord. When I plugged anything that was plugged into the laptop in to anything else (power cord to the printer, USB to my phone), my DisplayPort would shut down until I unplugged it and plugged it back in.

I ended up buying a better-quality DP to DVI adapter, and the problems went away. Are the two DP-HDMI adapters that you are using the same brand/quality? If so, you could try picking one up that's completely different, and seeing what happens.

Good luck!
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[IanWalker]

Okay, so I used to have a similar issue with my G5 Powermac, and I found this:
http://hints.macworld.com/article.php?story=20051110105729848
and several other threads elsewhere about it.

CHUD Tools allow you to diable processor nap, which is what was causing it for me.

Worth trying. I don't have DevTools installed now, but you can nab XCode from the App Store in Lion or newer. Its a 1.6GB download, so I'm downloading it right now, but it'll be a few minutes before I can check if that feature is still there
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