833 making odd noise in 2nd gear only

In my 340 Duster with an 833 and 3.23 geared 8/75 rear, I recently downshifted at around 20 mph, and did a nice WOT pull to about 5500 rpm. Since that stunt, when I shift into second gear and release the clutch, it has a systemic clang-clang noise as if it banging in the bell housing, that increases in frequency and volume as RPMs increase.

It does not seem in time with the frequency of the RPM or the rear end. For example, at around 2000 rpm, it literally makes the clang clang in as much time as it takes to say it (1/2 second), but then 1-2 seconds of silence, and this repeats as long as the clutch is engaged at a hold speed or accelerate rate. If I decelerate, it stops. If I disengage the clutch, it stops even while still in second.

It does not make the noise in 1st, 3rd or 4th.

Linkage bolts are tight.

Thoughts?