Buzzing could be caused by either excessive wear to first fret - i.e. that the F fret is always too low... however, if the neck relief is too far forward, this may also cause the fret to buzz. Measure the relief to decide if this is the case, and *maybe* try a small trussrod adjustment... In my experience, Warwick alloy fretwire holds up quite well... but if you're not sure definitely get a professional to look at it!
1991 Warwick, I guess that means MEC as opposed to EMG? Could be soldering, or knackered pickup..... however if it's a 4 string SS1, then you'll have a P in the neck, which will always sound louder, so to get the two to balance, you may actually need to try lowering the P.
Hope this helps!