I have the same issue and curious if someone knows for sure.
I have been told that it is the brakes adjusting because it does not happen after I am moving. Try it after it runs for a while and see if it still does it.
Should be 4-6 clicks pulling up on the lever. The rear break shoe clearance needs to be adjusted first (BR-38).
Parking Brake (BR-14). (a) Loosen the lock nut and turn the turn backle until the lever travel is correct.
(b) tighten the lock nut - 48 inch lbf. Then check the Bellcrank. Make sure that the adjusting bolt on the bellcrank is not apart from from the backing plate
I had the exact same problem after I had aftermarket pads placed by a local guy. It was driving me crazy, and I was ready to take it to the dealer but it resolved spontaneously. It would start while reversing after I first pressed the pedal while backing out of the garage.
I love how on this forum anytime I have a question, someone has already asked it. And someone knows the answer.
I had this same problem, and it would go away every now and again. Pretty sure its my joints. After driving through a few rivers and spraying the joints with a little wd40, figured it was the joints. Gonna grease up in few days.