Connection speed fast once I start Fiddler

I have two laptops, one of them has no problems whatsoever when it comes to browsing the internet, everything is speedy and pages load as expected.

The other one however, is a nightmare. Pages load slow, and it looks like the browser just sits there and waits a bit before it starts to load pages.

So I installed Fiddler to check the requests that are happening and how long they take to complete.

However, once I start capturing using Fiddler, the browser becomes speedy, and the pages load more or less as on the first laptop.

• So once Fiddler starts, browser speed is normal
• I experience this behavior in all major browsers (chrome, IE, and firefox)
• I have checked the internet options, and there are no proxies configured

Can anyone explain me what is going on?

I think it's a virus that "hooks" queries of your http port.
If Fiddler uses the same hooking method, it can stop hooks of another "hookers" (in this case - virus).

Thoroughly check your OS for viruses using powerful antiviruses such as Kaspersky IS or Norton IS.
Use Sysinternals' Autoruns.exe to check ALL autoruns (because MSConfig doesn't show ALL autoruns). Also use ProcMon.exe to see which programs are running and which are using internet when you're connected to the net. These tools will help you to catch virus.