Hard drive light flashing

My hard drive light flashes every few seconds as if the computer is
reading/writing.

I have read responses to similar questions, but think my problem is
different. Here are the facts.

I copied contents of one of my drives to a different drive, including
reinstall of Win 98 on this second drive. When I make the new drive the
master and the old the slave, I have this problem. It does not happen with
my old drive.

This happens even when I am not on the internet or doing anything else at all.

Thanks.