What is this rattly chattering noise from underneath?

[240Lemonade]

I know that it has some valve tap, that I can deal with, but if you listen beyond that you can hear a lower rattle/chatter/rumble. At first I thought it was a rod bearing or a crank bearing, but it is not really noticeable until the engine is warm, under load and up to 2000 rpm, and this noise does not really keep time with the engine. It is more of a chattering noise than I would expect a bearing to be. The engine has good compression, all between 197-215 psi.

If this information is useful to an online diagnosis: the transmission will not kick into OD. No, the button is not depressed, but the "OD OFF" light still comes on when I do press it, but nothing happens. So I really don't run it past 50mph = 3000rpm. I am assuming that it is the OD solenoid but I have not investigated, I just thought that maybe someone in "the know" would be able to use this info to help me out.

Does anyone have any good council? As I lie on the couch complaining about my issues. Speaking of issues, don't forget that Sunday is Mother's Day.