Howdy. Haven't had to bother y'all for a while, mainly because the Little Blue Car has been running pretty well.
Until recently.
Last month the purge valve failed, the instrument panel lit up like a Christmas tree and we limped into a Chevy dealer to get that fixed. And, as a bonus, discovered that the timing chain guides had failed too, stretching the chain, as I was told. (And I believe the diagnosis too — the engine had been "growling" at low RPMs for a couple of weeks prior to this mishap.) A rather pricy first-time encounter with this dealer, but it was fixed.
That was four weeks ago. But also in this past month I've noticed a "tapping" sound from the engine, coming on around 2000 RPM and especially when cold. The noise does diminish a great deal after the engine gets warm but never entirely goes away.
Us old motorheads used to know a sound like this as "valve tap," and would grab a couple of wrenches and a feeler gauge to check the clearance between the valves and the rocker arms. But overhead cam engines aren't supposed to have this problem, nor have this kind of rattle.
She's due for an oil change in a couple of weeks and I was thinking about a slightly thicker oil. Winter's almost finished here in SE PA and moving from 5W-30 to 10W-30 shouldn't be that taxing on the engine, which just turned 129,000.
Any ideas from this well-versed group?

 

The valve tap as you describe could be a weak chain tensioner, a broken front timing chain guide or guide bolt. Listen to it after the oil and filter change.
I wouldn’t very from the prescribed 5W30 engine oil.

 

Or, injectors. There are no tappets to make clicking sounds.