97 Grand Am - Mystery Stall

My sister has a 97 Pontiac Grand Am 2.4L DOHC with 135k mi.

Yesterday, I was told this story:
She was on her way home from work and her engine started making “A Noise”. She pulled over and checked her fluids and found herself low on oil and coolant. So, she got some oil and coolant and filled both to their proper levels. The “noise” did not go away, and the car stalled about a quarter mile from her house on her way home.

Here’s where I come in…
I visited her car yesterday and used a scan too to see what codes she had set. I was surprised to find no codes stored. I checked her fluids and all was good, so I attempted to start the car. The car started normally and ran smoothly, but I heard a ticking noise. Kind of like a valve tick/ (I also heard an old exhaust leak, but that’s not relevant to the story) I watched the scanner for a while and found nothing that would suggest a stalling problem. No misfires, normal air and fuel numbers. Etc… I go to investigate the noise and It sounds as though it is coming from the exhaust side valve area. (Transverse mount engine, rear side as mounted in vehicle)

I am iffy at non-computerized engine diag and even more iffy with common GM issues.
I’m ready to rip the top end off and pull valves, but I’d like an opinion from someone who knows better before I go and waste my precious Saturday.

bump