Hi, all.  Long time no post.  Of course I log in because I am looking for insights.

Riding my gravel bike today.  It has di2 ultegra components.  Sounding a little noisy at first and I thought chain rub but heck it got a full tune not long ago so that's a little odd.  It started getting nosier as the ride went on, particularly going up steeper hills.  As I continued it got worse and was present with any significant load on the pedals/drivetrain (e.g. pushing the pace on flatter terrain in a bigger gear).  Seemed to be present across the gear range and was clearly not just chain rub by this point.  Kind of a chunk, crunch noise at its worst.  if I pedaled just fast enough to keep pace with my speed on flats, no unusual noise, apply more pressure, noise is back.  Time to turn around, this thing sounds like there is a failure coming (I did get off, flip the bike over, turned the cranks etc. nothing weird seemed to be going on, cranks were stable in the BB etc.).  A couple times when I was in the small ring here was a sound like the chain had dropped from the big ring to the small ring and I thought maybe I had a sticky/dirty link that stuck now and then causing the chain to rise off the small ring then slap back, but that wouldn't explain the almost constant noise.

Okay, now to the best part, the last mile home is up a long hill with pitches reaching 12-14% in short stretches.  It is nasty hot and humid and I am tired so just focusing on finishing the hill when I suddenly notice the sound is gone while I am under conditions when it should be at its most present.  When I got to the top I shifted into the big ring and some smaller cogs and laid into the pedals and the noise came back but not nearly as severe.

Any ideas?

Thanks.

Hope you are well.