Bottom End Noise (Forged)

In my personal motor, (VG30DETT) (Wiseco Pistons) I am having an issue that seems to be quite unusual. Perfectly quiet on start-up and a slight metallic sound at operating temp only. (Sounds like a light piston slap/ Sewing machine) Textbook oil pressure, no shaving in filters or oil, Only noticeable at idle. Over 4k miles on it now and runs strong. Also utilized a torque plate for boring process and double checked cylinder wall clearance to .0030 nominal (per Wiseco). Could this be a metallurgy issue in the manufacturing process? Have any of you seen this before?

I have also noticed that if I probe the block and transmission with my stethoscope, I seem to be hearing the same ticking come from the base of the bell-housing where the output shaft bearing is located..

How likely is it that it is transient noise coming from the transmission, into the crankshaft?

Also: On Carrillo rods with ATI HB damper.

Thanks for your time.

That's a weird one for sure. If it's piston to wall clearance then you'd almost certainly notice it when the engine was cold and it will decrease when the engine warms up. Is the noise in time with engine rpm? It could be a valvetrain related noise possibly. It could be from the transmission or the release bearing but it should be easy to rule that out if the noise goes away when the clutch is disengaged.

Same thoughts here..

That's why I have stumped myself. Yes I can hear it go up with RPM, (but only not under load) which made me think more towards the trans/clutch pack as well. While under load, I hear nothing.

It's hard to make a solid recommendation for how to progress here. It may be nothing (or at least nothing engine related), however it could also be the first signs of something more sinister so it's advisable to spend some time getting to the bottom of it for peace of mind (it could also save you a lot of money if it is the first signs of imminent part failure). Just as a thought, engine load will often mask aspects such as an engine bearing related noise and this is usually more apparent on a free rev.