Wireless speed drops to almost halt, Windows 7 64 bit

I just built a system with Windows 7 Home Premium 64 bit with a Gigabyte WP30N wireless card.

When connecting to my router (a Netopia 3357), the network speed is initially OK (500kb/s), but then drops straight to a consistant slow (20kb/s). The time it takes for the speed to drop is anything from a few seconds to a few minutes. The slow speed stays.

The odd thing is, if I disconnect and reconnect to my router, the speed is back to OK till the same thing happens and it suddenly drops again. This happen everytime, no matter what I do. Transfering a file with ftp from the command prompt or some web browsing is enough.

At first I thought it was the card, so I removed it and tried two different USB wifi plugs (Sitecom and D-Link). Same thing happens. I have several other computers (running XP) with wireless connections to the same router, that have never had any problems.

So I reinstalled Windows 7, thinking perhaps I messed up something. I did a clean install with no added drivers (Windows 7 installs a driver for the Gigabyte WP30N card automatically), first thing I do is try to transfer some files with ftp, and the speed still drops! Windows 7 Update found a newer driver for the card, but it made no difference. I also tried Gigabyte's own driver (Ralink), also made no difference.

I am totally clueless and this is driving me nuts.

Anyone got any ideas?

Have you tried changing channels on your router? You might be getting signal interference from another appliance.

I tried a few other channels now, within the 1-13 range, but it didn't do anything to the problem.

I seem to have fixed the problem, atleast I haven't had a speed drop for half an hour now. I disabled the LLTD IO mapper which among other things supposedly determines network bandwidth. Sort of makes sense.