EGGZACTLY MUNDO!
When high current demands hits due to the low HZ bass excursions, current starvation can actually be seen as a dimming of the lamps (if lamps are on). Large capacitors release energy as needed to smooth out those bumps in the energy supply.
If anyone has an RX-7700, then you already KNOW what I"m talking about. Crank it up past 1/2 way and it will begin to sound a bit crappy, especially with the bass up. With the dial lamps on, you can actually SEE the weak notes. It's running LOW on juice. Unfortunately, I have NOT had the chance to address that issue on my 7700 yet. But suffice it to say that a cap replacement is gonna be Priority One on my Panny's.