I've occasionally noticed that on a cold start the power steering pump will be a bit noisy. I've only noticed it a few times over the past few years, but yesterday I was under the hood right after starting the engine after it had sat a few days, and I recorded this horrible noise it was making.
The noise went away after the engine warmed up. This is on my 98 Mazda 626, and I'm wondering if maybe this indicates a problem with the PS pump that could be putting mechanical drag on the engine and causing it's low, rough idle under load.
EDIT Jan. 24th, 2018
I checked this morning, the PS was 12*C/53*F and made no noise on start up. I noticed a few small bubbles right at start up, but that was it.