krispy

Not sure what this is, but I have a noise that started intermittently a few weeks ago that sounds mechanical/spinning/whining that starts at idle sometimes. Happens regardless of coolant temp, might be oil temp related but haven't taken any long drives (15 min trips), has not occurred as much as it gets warmer out. You can hear it from the driver seat a little better than you can with hood open (the DI ticking is louder next to engine and drowns it out). It doesn't happen all the time, but when it does I will come down to idle and it will start ~2-3 seconds later and keep going even after starting back out in gear. It's somewhere around 40-60 Hz per spectrograph tool on phone ~2000 RPM.

No DTCs, no power loss, I pulled the valve cover & everything looks great (cam lobes/rollers, pump lobes, timing drive, no sludge), no instability or impact on idle quality.

I haven't had it happen at high volume since I got a mechanics stethoscope, but when it was quiet I thought I hear it somewhere near cylinder 3-4 when listening to valve cover.

I'm wondering if the LNFs have any tendencies to get sticky hydraulic lifters as the engine gets older; that's about the only thing I can think at the moment.