[Cherish]

Yep! Very much trial and error, as every pig is different and has a different personality.
One of mine for example, The Doctor, often makes a distressed noise. It's relatively quiet, compared to a wheek for food, but it's very high-pitched and quite quick (sorry if that's a bit vague- it's difficult to explain their noises sometimes!)
When I first got him, I used to pick him up for a cuddle, and the distressed-sounding noise would continue, so I'd put him back in his cage to avoid upsetting him further. But as soon as I put him back, he'd squeal the house down.

Now I know that the distressed noise, when made by The Doctor, usually means; "I've started a fight with another guinea pig, and now I regret it because I'm coming off worse. Rescue me, human!"
The noise continuing while I hold him, is his way of complaining and telling me his troubles; "...and then I head-butt him, and he head-butt me back, and he's got a bigger head than I do!"
And the squeals when I put him back in the cage means; "WAIT! WAIT! What are you doing, human? He's still mad! I need consoling!"

Whereas when The Professor makes the same distressed noise, the last thing he wants in the world is to be picked up and cuddled, he just wants to be left to complain alone.