This started earlier this week...

I'm driving down the interstate, I drop down a gear to pass, and suddenly my alternator warning light - and only the alt. light - starts to blink. When the revs drop back down again, it stops. The voltmeter shows a steady, greater-than-battery voltage the whole time. Then it happens again. Then I notice it happen over hard bumps. I made sure the red wire on the back of the alternator was secure. In the next few days, I noticed the following other related/unrelated curiosities:

1) It seems to only happen when the car is warmed up, and the ambient temp is above freezing. On my morning commute, with temps in the 20s, it never happens - coming home, its near 40 and it starts up after ~8min on the highway.

2) Once I see it happen, I can keep provoking it even at a full stop by revving the engine.

3) As stated above, the voltmeter never even flinches. Yet my oil temp and oil press gauges DO go slightly erratic when the light flashes - almost like they are experiencing an intermittent short on their power circuit.

4) Just today at lunch, it happened again, and I could almost hear a litle 'zapping' sound behind the instrument panel. The origin of the noise is very much in question, however, due to the loudness and hard ride of my 240.

Sorry for posting this w/out doing much investigation, but I'm hoping to get any helpful opinions on the problem before I get home from work. Does this sound like a possible bad diode/diode pack, worn brushes, or do you think maybe there is a short in the dash? TIA...
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Speed Racer, '83 240 R, '74 164 E, '93 940 OL1 (Manchester, CT)