This is model fatigue in the low end. Suno holds a clean mix for the first couple of minutes, then the bass frequencies start stacking — each new section adds a little more low end until it's all mud. Long instrumentals expose it worst because there's no vocal to anchor the mids.
1. Generate in shorter chunks. Get 60-90 seconds of clean instrumental, then Extend. Each Extend re-anchors the mix instead of letting the bass snowball for 4 straight minutes.
2. Write 'controlled' into the Style. Words matter here: tight controlled low end, clean bass, no mud beats deep massive bass every time. 'Massive' and 'deep' are literally instructions to pile on bass.
3. Use the Exclude field: muddy, boomy, distorted bass, low-end rumble. Don't write 'no muddy bass' in the Style box — put it in Exclude where negatives belong.
4. Fix it in stems. ... > Get Stems, pull the bass stem, and high-pass it around 30-40Hz in any free DAW. That alone usually rescues a muddy generation — the mud lives in frequencies you can't even hear as notes.
5. Leave space. If your prompt lists bass, 808, kick, and low synth pads all at once, Suno layers them all. Pick two. You can always add the third in a Replace Section later.
Good luck! Hank founder of SonorixPG