What is the reason for freezing during network activity?

Question

Iron

Good day everyone!
Already broke my head, I can not understand. Windows XP SP3. Intel Quad Core Q6600. As you work, the computer gradually begins to slow down at the time of network activity. If a site with a large number of pictures is loaded, the music slows down, the mouse pointer freezes, i.e. the system is physically hung up. If you look at the loading of processors, at this moment the "core time" is shown in red graph. As soon as the data transfer indicator stops flashing, the hangs stop.
This is definitely due to data transfer through the network interface (twisted pair). The situation is the same with the built-in network card and with the specially purchased PCI. The problem is completely cured by a reboot, but after a day or two it gradually begins to appear and worsens over time, the feeling is as if the glue is hardening. What program is downloading the data, no matter what the browser, what the torrent, what even FTP is the same.
I checked the system from viruses and trojans far and wide, I could not find anything intelligible ... It costs NOD32, COMODO Firewall. Launched CureIt. I don't see anything.
Already broke my head, tell me, pliz? .. Maybe I'm looking in the wrong place or looking badly? Thank you!

Answer 1

> If you look at the load of the processors, at this moment the “core time” is shown in red graph
Look at which particular process has the honor to eat the processor.
The probability that this is a firewall or antivirus is quite high.
The fact that the problem is of a cumulative type may well be due to clogged caches of these programs.

Answer 2

Have a look just in case:
Half-open TCP/IP connection
Generic tcpip.sys patch