There are some YouTube videos of noises though some of them I think really ?
There's no concrete view on "Singing" (chirping like a bird) some say its distress. Its a weird noise for a rodent. We've had pg pigs sing, one of my pigs (don't know which) sang on the day we had GP5 PTS .It might have been GP5 death song?
Most recently our boar sat in the garden run just singing
. Not pregnant, not dying, not distressed. Just him being him.
Purrs can be brisk Hello, whas upp
Or a boar rumblestrutting , body rigid and sashaying like a serpent.
GP6 purrs when he smells DD jumper after she cuddles the sows. He sniffs her , pulls her clothes with his paws. He lives right next to the girls, he's not deprived of their smell .
When we go to the Pighouse GP7 usually squeaks the loudest , a proper wheek wheek wheek Here's Mum with brekkie call
A stressed piggie (like when I'm cutting the claws) go quieter , we don't get the full on vocals then. Its more body language , pulling away, shrinking down, head down.
GP8 doesn't squeak but she purrs if she's cuddled.
GP2 never squeaked to my knowledge until his last breath (he died on my lap and did a long wheeeeeeeeeek when I moved him slightly
) but he did brisk little laughing purrs
If they're angry they chatter their teeth , like a grinding side-to-side of the jaws. Head up , arched back.
We played piggie noises to our trio a while back (GP3 GP4 GP5) , my little Himmy GP5 went sauntering off to investigate "Bugger off you interloper"
GP1 purred along to a game (Animal Crossing) DD had , it was like an Indian sithar, GP1 must;ve thought he was a mongoose 
With the ramp , make sure it shallow enough and secure . Maybe put some sides on it to make it enclosed for security. They're not natural athletes so they might've been put off if they were jostled or fell off the ramp.