kind of noise...
Though I can't describe the sound any better than, valvelike, I hope this other info may help- thank you. "Valvelike"- a certain sound I have noticed in some cars my whole long life!! Please, no flame! ( Since writing most of this, I see Silver.... mentioned rods!! )
The sound first started at 55000mi when I needed a head gasket replacement.
After that ( dealer ) job, very quietly I would notice a faint sound on warm up; not when idling, but only under load, 2000 rpm's and higher. I now have 90,000+ and the symptoms are all worse.
On warmup, under load, meaning driving it:
When engine reaches around 2000rpm on up, I notice a sound that sounds valvelike to me. Sorry, no better terminology!
If I back off the throttle, it drops out, if I give it the gas, it returns, instantly. When I sit at a light, I don't notice it, it becomes obvious under load.
One ray of hope, it doesn't seem to be consuming much oil ( Mobil 1 )....
I brought it to idiot dealers, and they "couldn't hear it", supposedly.
Why does the sound eventually disappear, after 5-10 minutes?
Heat expands things, is one factor, right?
Oil thins, is another
If not valves, what? The oil not getting "up" in the engine for some reason- oil pump, oil filters?
-It is now slightly audible even OUT OF GEAR- a friend detected the sound just standing outside car, next to the engine last month.
-It used to not reoccur unless car sat for many many hours- NOW it happens after sitting for just a few hours, and is significantly louder.
i believe dealers shoddy workmanship, helped cause the problem with the head gasket replacement.
Stock 2003 "Sunburst" Spec V formerly.
2006 3.5 Alt 5 speed, formerly
2005 Subaru Sti