You need to tell us more about where the humming is coming from (rear left , front left or somewhere else), what the record player does / doesn't do. How loud is the hum?
It will help for you to remove the top panels which will help you diagnose what is going on. This is easy enough I think there is a post somewhere round here that explains how to do it.
Not sure if the 4004 ever had ac motors? but this is a possibility..
Not sure about a repair engineer I know there are a couple of folk in the states that know B&O well, and it would be worth sending to folk like this if you are unable to tackle the fault yourself, rather than send to any old repair outlet.