Wow, this is a tough one. Do you get the same buzzing noise if you disconnect the isolator from your receiver and listen through headphones to the MobilePre?

I just checked and there is no buzz in my headphones. It's only when the audio passes through the Receiver that the buzz occurs. I believe the problem deals with the 2 separate power cords. The cord to the receiver and the cord to the computer causing the loop issue. The MobilePre, running off power from the computer through the USB cord, would not have any buzzing out of the headphone jack.

But I would assume that the isolator would, well, isolate the two sides. Is this isolator a transformer? What happens if you directly connect the MobilePre to your receiver (no isolator)? Does the buzzing get louder?

What about plugging the entire system into one power strip/power conditioner? Have you tried that. If you are using two different outlets you may have a difference in the ground potential. If that's not it have you tried changing the distance between components.

To answer CharlyD's post, the isolator is from Radio Shack...it's the one where it looks like RCA cables passing through a cylinder...the cylinder being the ground-loop isolator.

When I switched the cord for one without the isolator, not only was the buzzing louder, but it was in both speakers and it had a sort of "wah" effect.

To answer Mrlowry's post, the entire system (the computer and receiver) are both plugged into the same surge protector which in turn is plugged into a -4 dB noise reducer. the distance between the computer and receiver has to be at least 3 feet. being as though my receiver is on a wheeled shelving unit, I did change the distance and the buzzing didn't change whatsoever. The buzzing is still in the right speakers (of both set A and set B) and it's very annoying.

Thanks for the input so far.

There is a large community of folks who use a BFD (parametric equalizer) to flatten the response of their subwoofers. The BFD is notorious for introducing a hum in the subwoofer. HERE are some tried and true solutions that may be helpful. Best of luck.

RG

Thanks the the post. I read a a lot of the posts being made at the link you gave me. I actually was intrigued by the very last post. Behringer (a company I have a few products from) makes a 2-Channel Hum Destroyer for only $20. I think I may purchase that and see if it helps the situation at all....if not it has a 30-day money back guarantee. Hopefully it will work.

The Behringer box looks appears to provide the same function as the RS isolator you're already using. If the Behringer box works, I hope you can return the RS device. Your laptop is apparently generating lots of noise referenced to the AC line. The RS box seems to have too much coupling from input to output to block this noise. If the Behringer box doesn't do the trick, the next steps might be a power isolation transformer for the laptop or a USB isolator, both of which are a lot more expensive. Good luck and let us know the outcome.

Do you get the same problem if your computer rig is hooked up but you are playing another source? Have you tried switching left for right interconnects to see if the problem switches sides? What purpose does the M-Audio MobilePre serve? Can it be eliminated?

If the Behringer does the same thing as the Ground-Loop Isolator I already have on my RCA cables then I doubt it will do the trick.

No matter what I am playing, if my computer is hooked up the buzzing is there. If I switch the receiver over to my DVD player or Xbox the buzzing isn't there.

When i switch sides (right to left, and left to right) the buzzing is STILL in the right side. That is why I initially thought it was a bad wiring job. I did look at the wires, but noticed that the buzzing was coming through BOTH speaker set A (Bose 351's) and speaker set B (Small JVC's).

The M-Audio MobilePre is used for working with ProTools. It's a recording program that a standard in the music industry world. The only way to open and use the program is to have a ProTools certified Audio Interface attached. If I am listening to iTunes, obviously I don't need it, but when I work on my audio projects in ProTools, it needs to be there.

But even if I eliminate the MobilePre...the buzzing is still there.

A guy at radio shack told me that this item, which costs $100 is the only way to make sure all your electronics don't have noise interference

Surge Protector

I am hoping to not have to spend a lot of money trying to fix this, but I have run out of ideas.

That won't help. The hum in one channel means that it most likely isn't an electrical thing. Do you have an extra inputs on the receiver? If so try moving it to that one. Perhaps you have a bad input on the receiver.

I tried moving the red/white RCA cables from CD (where they are usually) to Video 2, Video 3, and TAPE....each input has the exact same problem.

What I forgot to mention earlier, is that the power cord for my laptop is new. The old power cord, which was grounded (three prong) broke and stopped working. When I had that cord I only got a few ticks and pops in the right speakers. Now that I have an ungrounded power cord (2 prong) i just get a constant buzz.

I also, just for kicks, switched my USB cord with a sheilded USB cord (one with the barrel looking thing around the cord). It changed the sound of the buzz just a little. Buzz seemed to lose a little high end, but the buzz was still there at the same volume.

edit: I just did some experimenting and found something out, but I am not sure it will help.

When I switch the outputs of the M-Audio (left becomes right, right becomes left) the noise still comes out of the RIGHT side

When I keep the M-Audio outputs the same, but change the inputs on the Receiver (left becomes right, right becomes left) the buzz switches from the right side to the LEFT.

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What I forgot to mention earlier, is that the power cord for my laptop is new. The old power cord, which was grounded (three prong) broke and stopped working. When I had that cord I only got a few ticks and pops in the right speakers. Now that I have an ungrounded power cord (2 prong) i just get a constant buzz.

Go out and get a shielded, with ground connection IEC power cord for your laptop. The "ticks and pops" you were getting previously were likely due to the implementation of the USB interface on your M-Audio box and can't easily be fixed.

Crap, so there is no way of fixing it without replacing the cord?...damn. No wonder the cord was such a good deal. Here is what I bought. Cheap Replacement Cord

and here is what I should buy?
Better Power Cable

I looked on Apple Official store and all I was finding was 2-prong power cables since I guess they are switching towards that. I found a couple replacement part websites that I could potentially use to find the 2 pieces of the original power cord.

Is there any way around the cord issue? or is it buy a 3-prong cord or deal with the buzz?

Sounds like you replaced your original power adapter with a cheaper brand that is far more noisy (RFI/EMI). All these power adapters include switching power supplies that absolutely require good filtering and shielding especially for audio applications. I haven't researched it, but I'll bet there are laptop power adapters out there that target audio appications. But I'll also bet they're not cheap. Of course, make sure the next one you buy has a generous return policy.

Yeah, I found a bunch of good power cords for like HP's and Dells. It seems like powerbook's and macs don't have a large selection....I am going to continue to look and see if I can find one. If I have to pay more money for a good cord I will, cuz then I feel no matter what setting I am in, the computer wont be the culprit of noise interference.

I haven't been able to find any "good" replacement cables, but I found an article at Apple.com that tries to help the situation. Apple's Take on Ground Looping

I checked out some of their solutions. Some of those DI boxes seem like they could do the job, but at $130 I wish I KNEW it would fix the problem.

also as a side note, a while ago I had a really old crappy external monitor hooked up to my laptop that caused the same type of problem. My uncle recommended me taping a bunch of shielding beeds to the monitor cable that are usually found in the monitor to make the cord shielded? It was a long time ago and I don't remember what "beeds" exactly he was referring to...but maybe taping shielding stuff to the power wire could help?

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I don't remember what "beeds" exactly he was referring to...

I suspect he meant ferrite beads. It may or may not fix your problem but at a buck or so a pop it is certainly worth a try!

actually now that you mention it, I think thats exactly what they were. He works for a big electronics company. I will give him a call and see if he has a bunch lying around..which I believe he does.

I still am keeping a look out for a good power cord. All the ones I have found are made cheaply. Most people don't use their laptop the same way I do.

thanks for the input so far guys.

Rather than beads, what would be more effective would be a ferrite doughnut. Ideally, you would be able to loop the AC power cord end of the adapter through the doughnut a couple of loops. There are also clamp on ferrite noise suppresors that would just fit around the cord.

so If I can get my hands on ferrite...that could potentially minimize the noise?...I will give a phone call to my uncle this week at some point and see if I can grab some whether it be beeds, doughnut or whatever.