Since you've already explored a range of string instruments, and are looking for something "different," most likely a wind or percussion instrument would be in order.

In the "percussion that can carry a melody line," the most portable would be one of the "xylophone" types used occasionally by marching bands. They're usually laid out like a piano keyboard, and since they're mostly in higher piches, would probably cut through the noise pretty well. Cheaper ones may have limited range, but they are available with a couple of octaves or so.

With wind instruments, and your past whistle experience, the flute, oboe, and saxophone families would likely be easiest to play, since the "register shift" is an even octave.

Alto and soprano sax can be pretty loud and are in a high enough register to cut through the mud. Lower pitched (and larger - less portable and generally more expensive) ones might be less audible in noisy places when played alone.

Standard flutes aren't known for "cutting through" the noise, but a picollo can really scream over almost anything.

Clarinet family instruments shift registers by 3/2 octave so there's a bit of finger transposing to do when you cross the shift point. They tend also to be a little less tolerant of sloppy fingering and embouchure technique, so they might (or not) take a bit more practice to sound respectable.

The common sax and clarinet family instruments are in Bb or Eb, which wouldn't be a problem if you're doing solos, but would perhaps require transposing to "less easy keys" to play with others.(?)

Most of the brass instruments rely strongly on lip control to get the right overtone plus key changes to get the right note, so the "fingering" is somewhat more complex to learn in the beginning. I'm told it becomes "natural" with only a little practice, but I've not made the attempt.

Most of these "standard instruments" are a bit expensive if you're looking for something to play concerts with, but used instruments can be reasonable if you can sacrifice some of the niceties. The xylophone/glockenspiel might be the most likely choice for something you might pick up fairly cheaply, although that depends a lot on your local market.

Of course, if you want to stand out in a crowd, it's hard to beat a Sousaphone, but they're not exactly hip pocket portable.

John