Mighty Mouse causes electrical noise on headphone socket of Intel iMac!

Question

Sorry for posting this again (it was originally a reply to another thread). I just felt it warranted some attention.
Mighty Mouse (and other USB optical mice) cause noise and interference on the headphone port in an Intel Mac!!!
In the other post it was reported that there was discernible electrical noise and interference when using the headphone port, with echoes, pops and a constant buzz and whine. I really noticed this as well, especially after the impressive noise-free headphone output of the Mac mini I had for 10 days before upgrading to an iMac.
I noticed that the noise changed from a buzz to whine when I moved and picked up the mouse. I've got my Mighty Mouse plugged into my keyboard. At first I tried unplugging the keyboard from the iMacs USB port and the noise stopped. Then I plugged it back in, and then removed the mouse from the keyboard. The interference stopped. I then tried plugging the mouse directly into the iMac. Again, that horrid buzzing whining noise and echoes. So it is definitely the mouse!
The noise changes when the mouse's scanning red light switches on and off and during movement.
I've then tried a second Mighty Mouse, the one I bought for my Mac mini. Same thing. And just now I tried another optical mouse, a mini-notebook one. The noise is even worse! It's quite bizarre as well, the noise changes in pitch the further I move it from the desk surface - its like tuning a radio!
Am I going to be reduced to plugging in a clunky old USB ball mouse to avoid noise through the headphone port of my 1 day old iMac? Can you actually still buy such a device?
Actually, can anybody report on whether the Apple wireless Bluetooth mouse causes electrical noise on the headphone port? And is the noise just on the headphone port or on the inbuilt speakers too? And on the headphone port's dual function as optical audio output?
This is not good. And I'm quite surprised it is something that has been missed by Apple's engineers. Or has it? Is this a known problem? Somebody should have words.
Can anybody from Apple comment? Do they frequent this place? I hope so.
20" iMac (Intel)   Mac OS X (10.4.5)  

Answer 1

Hello, I bought an iMac 20" today and ran into the same problem...and found this conversation (and the original thread) with a search for "iMac headphone jack noisy".
The problem is painfully audible on a pair of Etymotic Research headphones that I have on loan from a friend. These are designed to fit into your ears with earplugs that seal off the rest of outside sound, so it's practically like having an oscilloscope plugged into your head. Though the Mighty Mouse certainly aggravates the problem with the varying pitches of whine, I have to say it's just a noisy jack when compared with other devices I've plugged the headphones into.
For instance, my Powerbook G4 has some noise on the headphone jack but it's a soft hiss. There is no variation introduced by plugging in the mighty mouse.
However, on both the iMac and PowerBook G4 it appears that the electrical gain on the noise in the headphone circuit is completely independent of the volume level. This is not true of the iPod, where if you turn the volume all the way down while no song is playing the jack goes dead quiet. If I'm right that the volume is being done entirely with software on the computers, then I have become curious as to whether there is any way to control the electrical gain of the headphone jack.
Without such a hardware-level gain control in the iMac or G4, then if your headphones don't take much power to drive...the relative volume of the noise will be greater. So you can make this less noticeable with bigger headphones. I can't hear any of this noise when I'm listening on a pair of bulky AKG studio monitors (which are not particularly shabby in terms of frequency response or audio quality, though the maximum listening volume isn't very good without a headphone amplifier).
More expense, and hassle, just to work around a
problem that should have been noticed and rectified
before Apple released these computers to their eager
public.
In Fight Club, the main character faces the grim truth about how his automobile company handles recalls. The financial formula wasn't to recall a car just because they knew it had a fatal flaw, they recalled when the cost of dealing with lawsuits would exceed the cost of performing a recall. A lot of people in business think that way, and it's sad to suspect Apple is in that camp.
Still, engineering decisions are made within certain specifications and tolerances, and influenced by issues like price. So I accept that Apple cannot anticipate every audiophile application, and that there's a limit to the quality level the consumer interface can ship with. If someone wants better, they can buy a firewire or USB audio interface with higher-quality design.
The frustrating bit is that the only guideline we are given from Apple to expect on quality is "excellent", "engineered", and "pinnacle of design". Speaker manufacturers publish graphs showing the response of their system, which you can then test your unit against. Where is the noise limit specification for the headphone jack? Are we all stuck making individual appeals?
Since this problem depends on the headphones, you've got to prove that the headphones you're using are reasonable. Perhaps see if iPod headphones have the problem?
(Sadly I no longer have iPod headphones with which to test...)
Vainly crossing fingers for a fix.
At least at this point, it can pay off to speak up. My PowerBook mentioned above just had its logic board replaced in order to address a terrible whine that happened when the CPU was drawing a middle range of power. I couldn't really reproduce the horrible cases very easily until I finally found others who managed to figure out that the defect was so bad that some systems could play a nearly full volume musical scale on the analog circuitry of the power supply:
http://arstechnica.com/staff/fatbits.ars/2006/3/4/3059
Once I could demonstrate it, they fixed it. But the problem had been there since I bought the machine, and made it nearly unusable at times.
iMac 20" Core Duo   Mac OS X (10.4.6)   2.0 GHz, 512MB RAM