Guess that noise

I had that happen to me once; turns out in my case, the thrust bearing went out and the crank was moving back and forth. After a few thousand miles the noise went away as the TC bolts clearanced the softer engine-block material. Then it started to leak trans oil. Eventually the bolts took out the rear cam plug, and now I had two kinds of oil on the driveway.
it did the same thing; noisy on the power/ quite on coast.