Compression lost on #3 -possible causes?

I've a 2003 325i with 208k on the clock. It recently started running rough, and a compression check showed #3 low. Not zero- I just can't remember the number at the moment.

The car has no strange engine noises, although if it's been sitting a couple of days it'll lifter tick for a few seconds at startup.

No smoke out the tailpipe, black or white.

No oil in the coolant; no coolant in the oil. Not losing coolant, not burning oil at a high rate.

I'm guessing at this point that for some reason one of the valves is not closing fully.

The confusion for me is that losing compression usually means something catastrophic and noisy, or at least a blown head gasket with some symptoms (oil in the coolant, or vice versa)

Anyone seen a similar situation? What was the cause? Specific, not just "it has 208k miles". I got that part. I plan to remove the valve cover, so I'll be able to take a look at least at the top of the engine. Didn't know if there was anything I'd be able to see without a borescope.

I'm not sure what I plan to do with the engine yet, but I'd like to know some things to look for prior to the head coming off.

thanks.

Compression lost on #3 -possible causes?