I got all 5 heads, and when I return to Whiterun and approach Jorrvasrk Torvar appears as red dot on my compass and starts fighting me for no reason whatsoever. He's not essential, but I prefer not to kill him as this is obviously some stupid bug. Tried reloading - doesn't seem to help.

You could get him to chase you and you know how a wild swing can hit someone else.... he could hit a guard and then the guards could do it for you.

Errr ... He wasn't fighting you, he was fighting Silver Hands (who were the red dots)

When you get back from the witch hunt, Jorrvaskr is assaulted by the Silver Hands (although in my memory, the battle was over ?)

[censored] torvar.

Did you see if you have any bountys for whiterun? I remember having the same problem and decided to go to my crime record to find out that I had a bounties over my head on few cities. I paid my fines and when I came back things was normal again. For some unknown reason The companions acts like guards.