Possible infection or security problem?

Hello,
After a while surfing, the mobile broadband usb modem from my ISP transmits data (Upload and Download) quite a lot at once (especially upload), on its own for some time.

I cannot surf using the browser at all while it is doing that and after that. It will be very very slow to surf and after a while when the browser is done waiting, it won't display anything or "Server not found" message.

I have to disconnect the Internet connection to avoid further transfer (upload) of data.

(Already scan with spybot and malwarebytes but still happens. Not using the real time protection.)

Should I be concern about this event?
Do u suspect any malware, rootkit, data theft, etc. activity?
Can the ISP modem software do such bad thing?

-- Thankx in advance

Using: Windows XP Home (SP2)
AVG 8.5
Firefox
Windows XP firewall

Background services, which run without you seeing them, transmit your personal data while you are surfing. This may also include updates to your operating system, updates to your antivirus, update of flash player, etc...all this stuff is running because you installed it, and selected: "automatic update."
The speed at which this stuff runs depends on your internet provider speed, and the speed of your computer. If you are wireless, and trying to use internet, then double the time it takes, at least. (there is nothing faster than a direct connection), yes you can hook up the laptop with a direct wire, if you are wireless.

But getting back to it, there are multiple reasons why web surfing would be slowed down,
Test the download speed with Speed Test, to find out just how slow your internet is, before and after making repairs and corrections. This way you can see how much your repairs have improved the speed.
A dirty wire, a long wire, a weak signal through the airwaves, the wrong type of splitter, the wrong type of cable, and on and on can cause slow internet speed.

Loading multiple security programs, that were never intended to work together, and loading free security from the internet...can really contribute to a slow internet speed. Spyware, which is planted in your computer by downloads and websites you visit, can really slow it down too.

The number of processes, running in your system, especially when you have a single core processor or less than 1 GB RAM memory, can really slow it down too.

And so, measure your download speed NOW, as is. The plug the laptop into the modem directly and measure the download speed. Are you having a wireless problem? Or is it an internet provider problem?