Problem(?) with speakers

I have an Inox speaker system attached to my PC with two small speakers and a larger central speaker with the controls and attachment points for the other speakers and to the back of the PC.

When I first switch on the speakers in the morning I get a deep noise lasting for about 3-4 seconds. It is very loud and I am concerned that it may annoy my neighbours.

This has just started happening (the system is about one year old) and the odd thing is that it only happens after the PC has been off for several hours and not if I switch off and then on again. The volume of the noise is not affected by the volume or bass control.

Can anyone please suggest an explanation/remedy for this (in very simple terms please)

Thanks
Cozzielex

 

Thanks for replying Tim.

First I power up the PC then switch on the speakers. I always switch off the speakers when I shutdown the PC as they still hum and disturb me at night.