Best way to ‘quiet’ a truck for a stakeout?

[RustBucketRoy]

Got an old ’89 Chevy that runs fine but sounds like a demon gargling nails. Not ideal when you’re trying to keep a low profile outside a suspect farmhouse.

Looking for tips: sound blankets? Engine tweaks? Magic (the safe kind)?

Would like to avoid another situation where the target flees because they heard me idling three streets over.