Alternating low and high ping times on ADSL line

I have an ADSL connection at home. Pings times are usually acceptable right after rebooting the modem, between 15 and 60ms to google.com. A few minutes later they go up to 900ms or even higher up to 3 to 4 seconds. There is only one phone plug in the house with the ADSL modem connected. Nothing else uses that line. I asked my ISP about this for several times and all they can come up with is the dreaded "did you turn it on and off" response.

Problem: Internet surfing becomes horribly slow, watching video's is out of the question.

Diagnosing: Running ping (with and without -n to bypass DNS lookups) to google.com from the modem.

What I tried:

• changed the ADSL splitter
• bought a new ADSL modem
• changed the ADSL cable between the modem and phone plug
• checked down and upstream rates (modem says 8708 Kbps down and 1037 Kbps up, exactly what my ISP sees)
• changed from my ISP's DNS servers to Google's public DNS servers

A small sample:

PING google.com (74.125.136.101): 56 data bytes
64 bytes from 74.125.136.101: icmp_seq=0 ttl=51 time=16.792 ms
(...snip...)

3 minutes later, nothing changed:

PING google.com (74.125.136.101): 32 data bytes
32 bytes from 74.125.136.101: icmp_seq=0 ttl=52 time=2417.5 ms
(...snip...)

Anybody has some pointers on what I should try next? Changing my ISP is probably one possibility...

Solution 1:

Is this isolated to just one computer? If yes, I wonder if you might have some file share or torrent server installed (either knowingly or rogue software unknowingly) on your computer, and as soon as your machine comes online someone (or something) is connecting to your machine and using up all of your bandwidth. Look at the bandwidth you're using in the OS while this is happening to see if it's higher than it should be from just sending the results of the ping back to you. (However method it does- web browser?)

If the Modem can keep the ping going without your computer connected, Shut down your computer for a few minutes, come back and see if the ping times went back to normal while your computer wasn't connected.