Sorry for the late reply.
I had a AP-450 which had various other problems, including the buzzing resonance from the B2/B3 keys. In fact, during the last week, I've noticed crackles from the speakers, and sometimes, even that the whole speakers dont work for a while, and I have to wait for a while and then play them. The resonance is extremely irritating to me, especially since playing soft passages becomes all muddy, and the pedal only makes it even worse. I am planning to get it serviced, but reading your question, I wonder if I can replicate the problem anywhere other than my house, which is a major problem. Also, do your Bb2 and Bb3 have it as well? Mine has problems with those as well. And also, if I press the Bb3 and B3 together, it sounds like a helicopter has landed near my house. Let me just see if i can get it in a recording. Are you the same Rahul Rege who subscribed to my Youtube Channel? If so, shoot me a personal message with your email, and we can discuss further if you want.