Right now my D400 is in the shop, and I am waiting to rear back from them next week. They said it sounded like output transistors, but said now might be a good time to re-cap too. He was confident that he could get all the parts needed to do the repair. The shop has been in business for over 40 years and I have used them before, and trust them. I will keep everyone posted on what happens.
In the meantime I am still shopping for a new amp.