New 2011 iMac i7 slows Internet to crawl

[duteberta]

I got my new 2011 iMac (maxed-out i7) two weeks ago.* Since that day my Internet speeds have gone from 17 Mbps to 2-3 Mbps on all computer (clients) in my house.* AT&T Uverse tech guys have been out here almost every day since then troubleshooting every possible problem. They have put a new fiber OMT on side of house, new RG modem, put new plugs on CAT5 cables and confirmed that I am getting unobstructed speeds of 17 Mbps EXCEPT when my new iMac is running.

This occurs on wired Ethernet and wireless. We have disconnected the Airport Extreme to make sure that was not the issue. The best case scenario is when new iMac is on, I'll get 17 Mbps on the first speedtest, but on the next test will drop by half, then half again, etc.

Next door neighbors have good Uverse speed so it's not system-wide. No microwaves or other signals are running.* Troubleshooting has confirmed all CAT5 cables are fine.* I had PERFECT speeds on my old Mac and PC's prior to getting the new iMac.
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I called Apple support and they asked me to bring iMac into Apple retail store which I did today. Prior to bringing it to store Apple phone support had me clear Safari cache and do PR reboot- to no avail.
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I just wanted to document my situation here in case others are having similar issues and to garner any advice people may have.
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Thanks

 

[PaulDoFish]

Are you sure your new iMac isn't downloading any updates in the background? That's the only thing I can think of...

 

[aliensporebomb]

Ah -

Can you describe how you have this set-up?

What speedtest are you running? http://www.speedtest.net or http://www.speakeasy.net/speedtest or ???

Is there the possibility that the neighbors are jumping on your connection and bittorrenting themselves to oblivion? I hope your wireless is secured.