Pulsing oil pressure.... a bad sign?

[Stainless]

Hey all... something i've noticed on my oil pressure. When the engine is warm, and at low rpms (under 1000), the oil pressure pulses. I noticed it when I first bought the engine (olds 455), but now it seems to be getting worse. I don't know for certain when the motor was rebuilt, but there isn't a bit of grit or buildup on the rocker arms/valve covers, so I would guess not too long ago.

Usually, as you increase the rpm's, it smooths out, but now, it seems to be sticking around more.... also, it is fine when the motor is cold.... smooth at all rpms....

any thoughts????

Thanks!!
~Sean