Do penguins quack, or are they silent creatures? Do different species of penguin make different sounds?
“Hail Mary, mother of God…” 
And welcome aboard and say goodbye to your free time.
This site has pix and sounds of many different penguins:
When we were in Cape Town, my wife was bitten by a penguin. Namely, a Jackass Penguin, which is so named because of its loud braying. I can attest to the name is rather accurate.
…and if they quack - does it echo?
They sound pretty much like Burgess Meredith.
Aaaadrrghgh. Asaaarguugh.
Sorry. I can’t do it justice.
It’s kind of a “squish”, kind of a “crunch” - depending on how fast your driving…
Nah … I’d say it’s definitely more of a crunch !
Julie 
Well now that’s kind of personal, but anything in the name of fighting ignorance.
At times, very high pitched and girly. Which is okay, except for the fact that I’m bearded, 6’ 4", and roughly 260 lbs.
And I wonder why I always get weird looks…
Brrrrrrrrrrrr!
I’ve heard Yellow-Eyed Penguins in the wild, and they are pretty damn loud. I’d characterize the sound they make as sort of a long shrill whoop, although the page n5tp linked to will probably convey it better than mere words can do. However, you’ve also got to imagine a flock of penguins pointing their beaks straight up and shaking their heads while they let loose with this noise. Meanwhile, the sheep who share the field with them continue to graze …
New Zealand is a weird country
I recently read a great book about penguins called “Waiting to Fly: My Escapades with the Penguins of Antarctica” by Ron Naveen.
At one point he describes the various calls/warnings of the three species he’s studying (Chinstrap, Gentoo and Adelie), and they all seem to have their own vocal differences. Also, from my nature documentary experience, I seem to recall footage of penguin colonies included a deafening roar of constant vocalizations.
Great book. I recommend it if you can find it.
If you drop them off tall buildings, a kind of a “plop!” sound.
Otherwise, they’re moaners. 
Last time I heard one, he was reciting the sonnnet “High Flight”, by John Gillespie MacGee. But they’re also known to make a sound like “Vote Meadow Party in '84!”.
Of course there is a blog about that. The Penguin Blog.
Most of what I know is gleaned from the classic children’s book Mister Popper’s Penguins. According to this mine of accurate information, they say “ork”.
Youtube video “Penguin calls”