flickering and brown outs

This is in my home and none of my neighbors have this issue. Two of us get power from the same wire coming from one electrical pole. He says he don't have this issue either, but I must consider that maybe he just don't notice.

Occasionally (like once or a few times a day) lights flicker and/or go dim for one to a few seconds. It might happen once or repeat itself once or twice after the span of 5 or so minutes. Then it might not happen again for hours or until the next day. The filament bulbs are the only ones to dim. The LED and fluorescent will flicker, but not dim. I think that is because of the bulb's circuit capacitance.

The vent fan in the bath will audibly slow on occasion for a few seconds. Nothing else in house appears to be effected, but that might be because most other things here (like computers) have internal regulated power supplies to safeguard against this. Maybe it would occur with my blender, but i just haven't used it at the right time.

Ive confirmed that this occurs on four different electrical circuits. It was noticed one two, then I left the lights turned on for two more electrical circuits for the last two weeks and noticed occasional flickering in those circuits too. Both had fluorescent, so I swapped with filament and now I see flickering and brownouts, all just lasting 1 to a few seconds.

Everything in the circuit box looks good and feels tight.

I have my DVM left plugged into an electrical outlet, but I never get there fast enough to see the brown out voltage.

Ideas?

tks,
pa