Probably not out of alignment since you didn't touch it, but after 3 years, certainly could have "Build-up" inside the bank reset coil plunger. With the playfield propped up, reach in and manually work the reset bar back and forth over the bank. Make sure the reset plunger is traveling the fully intended distance in and out of the coil freely. If it isn't, take apart and clean the plunger and coil sleeve, re-assemble and try the same procedure.
If it is binding up, what usually happens is the reset coil bar obstructs the full travel of each energized relay, keeping some switches from changing state. In your case, there is a switch on each letter relay that when energized, breaks, and should turn the coil back off. There is not enough travel to break these switches so the coil remains on, (and buzzing). The giveaway is the fact you said ALL rollover letters are doing this, and from experience, the bank reset coil bar with all of it's parts and linkage, make this a rather common occurrence.