2007 Prius Tapping - timing chain or rod knock? (how to test?)

Hi all,

I have a 2007 Prius that just rolled over 250K last week. It's been a great car, and I have maintained it regularly. I change the oil every 5k miles with Mobil 1. At the last oil change, I noticed it had gotten really low on oil, and started to develop a tap-tap-tap while driving. It is more pronounced now, but still runs and drives great.

The dealership said it was a deep rod knock (spun bearing) and that I needed a replacement engine.

However, this dealership is notorious for bad/incorrect diagnoses, so I wanted to ask the Prius world out there if there was a good way to test this on my own. I realize I may be facing an engine swap, but if I could get away with just a timing chain replacement or something else, that would be great.

I have a mechanic's stethoscope. What should I be listening for here, or what else should I be testing? The oil looks clean.

Thank you!