Question about my Hammarlund

[ablethevoice]

As a few of you might be aware, I acquired my first (in a very long time) "real" communication receiver from the E place. It arrived slightly dented, but perfectly functioning. I'm having a lot of fun with the old man - actually, I'm 2 years older than it is so it's not that old...
Anyway, I've noticed a slightly odd behavior with the S meter: it reads signal strength and varies as the signal waxes and wanes in strength, but when there is no signal at all, the meter "pegs" at the low end of the scale. I've already precisely followed the procedure for zero-adjusting the meter as per the owner's manual, yet the meter still drops below zero in the absence of a signal - and only when the unit is ON. I would consider the possibility that I had overcompensated with the adjustment screw if the meter did that while the unit was OFF, but while unpowered, the meter reads at precisely zero. What might be happening in the guts of my old 145X to pull the meter below zero?