New laptop, new sound card, old power amp and speakers…. don’t seem to mix.

I have a power amp which is older than me.  When my laptop and it are plugged into the same power circuit there is a HUM :-(   Now if I run my laptop off batteries it works fine, so I think it might be a grounding issues or something.  My second set of speakers seem to work fine.. which in some ways good because I will have more room on my desk, however they don’t provide the same clarity as the others.  I’ve posted the situation on to a digital recording BBS which a frequent to see if anyone might be able to provide a solution… so will have to wait… otherwise I’m working on my newer old set of speakers.