I recently bought a 77 SFDR and had it fully serviced. When I bought it it had a fairly loud hum and after it was serviced it still has a fairly loud hum. Loud enough that I can hear it across a room. Two techs have said there's nothing that can be done about it unless I start replacing the wiring itself. On the other hand I've read in various places on the net that pretty much any amp can be made quiet. So, are some amps just more likely to have a louder hum than others, even in the same model, or should I go find a third tech?