buzzing noise coming from power plug

I have an acer aspire 1690
yes please pity me... anyways

My power plug is really annoying me.

When plugged in sometimes for no reason at all it will act like its not plugged in...
this switches like crazy (plugged in, not plugged in, in, not, in, not).. i can tell because
the brightness goes up adn down on my screen. so that is annoying

also, there is a low screeching sound that comes sometimes from my ac plug in...
if i jiggle it it sometimes goes away but its really annoying as it comes back in 1 min.

I have checked the ac plug and the male receptor within the laptop and they are both fine
anyone understand why this might be happening?

all i could think of is the connection from the male receptor is not connected to the motherboard
securely anymore but i checked that...

Yes it definately sounds like the power supply is acting up. If not still under warranty you could replace it with a same spec power supply.