*edit* Didn't realise this was in the UTAU section! Luckily most of these still hold up.
Some fun things you can try:
1. Set any parameters to extreme values. They're generally not intended to be used at 100%, so these create strange effects.
2. Add large, sudden, off-key changes in pitch. You'll get lots of odd gasps, yells, and generally surreal microtonal wobbling. For example, a dense group of dramatic pitch bends creates a raspy, gargling noise.
3. Try short, unnatural notes, and push the voicebank as far out of its normal range as is audible.
4. If you have the software, use the audio-to-midi function in Synthesizer V and convert a recording that
isn't of someone singing. This will allow you to see what different sounds look like in vocal synth software, and get some generally weird looking phonetics and pitch bends to take inspiration from. An alternative is Spotify's free
Basic Pitch midi convertor (although this obviously only gives you the notes and no phonetics).