Hi - New VR5000 - have a few questions

Hi,
 I recently purchased a VR5000 via a well known auction site.  I got it for what I think is a very reasonable price.
 

 I was the only bidder as the seller advertised the radio as having a fault.
 

 Now the radio has a manufacture date of September 2003.   It does not have the DSP.
 

 I tried the V/M and Pwr switch to see the version number but it did not come up.   Is there another way to find out the version number ?
 

 At some stage the radio has had the LCD screen replaced and the display is very bright clean and clear.
 

 Now to the problem.   
 

 The radio has a low level audio tone coming from the speaker.   It is only just on the level of being noticeable.
 

 It seems to vary in volume ever so slightly when the tone control is increased and also with the volume control of the sub receiver when the sub receiver is turned off.
 

 I have checked the seating of the cables etc on the various boards and am happy to delve further in the radio to fix.
 

 Has anybody come across this problem before and any suggestions would be greatly appreciated.
 

 Thanks,
 Mal
 VK3AZZ