AVG Free long start scanning

I installed the free AVG at my win XP, Pentium 4, 3 GHz, 2 GB RAM computer. Every time I start the computer AVG scans for 10 minutes and the CPU is at 100% all that time. Very irritating and I have not found a way to stop or shorten it. I would accept if it scanned a couple of minutes or so but 10 minutes at 100% CPU is too much. Is it really necessary to start with that long heavy scan? I have not done any changes to the settings in AVG.
So is there any possibility to change this behaviour?
Is Avast different? I do not want to pay for this if the long start scan can´t be modified.
Replies much appreciated.

Thank you, Lennart.
We'd request you to reinstall the AVG product to check if that resolves the issue.

Hi Lennart,

We're glad to look into this & help you.
Please let us know whether a window is displayed at startup stating that a scan is in progress.
If possible, share us the snapshot of it & screenshot of the task manager that shows CPU consumption as 100%.
Also, let us know whether there are any other antivirus installed on your computer.

Lennart, we're glad that the issue is resolved now.
It could be possible that a scheduled scan was misbehaving. We're sorry for any inconvenience caused and let us know if you need any further help.

Well, I reinstalled AVG Free and miraculously the long start scan disappeared. I have restarted twice now without that scan starting.
What happened? What could have been wrong before I reinstalled?
Well I am glad it disappeared and hope it won´t come back, knock on wood.
Thank you for the help!

Hi Lennart,

We're glad to look into this & help you.
Please let us know whether a window is displayed at startup stating that a scan is in progress.
If possible, share us the snapshot of it & screenshot of the task manager that shows CPU consumption as 100%.
Also, let us know whether there are any other antivirus installed on your computer.