Timing Chain Question

[SloMo]

Hi there,

New member here, proudly driving the Toyota Yaris for 19 years. It has 154,000 miles on the clock and generally runs smooth as glass, but over the last couple of months it's getting a little louder - not hugely - especially when it's idling, or just started.

Yesterday it was idling while I put some coins in a parking meter and the noise became so loud from it, I thought it was the air conditioning in the shop it was parked beside. I turned off the engine, and when I turned it back on, the loud noise was gone, and hasn't returned.

Does this sound like prep for a timing chain snap? Or if not, are there warning sounds before a timing chain dies? Is 150k miles a lot for a timing chain?

Many thanks in advance if you can help, I don't wanna lose old Bonnie Blue!