Motorcycle Repair: HD twin cam noise, rpms increase, rod bearings

Question
QUESTION: I recently bought a 2007 Road King with 30K miles.  I have noticed when the motor lugs at low rpms, like 45mph in 5th gear,there is a knocking sound synchronous with the rpms.  It is not preignition pinging. It disappears if I drop down a gear and bring the revs up. I have always associated knocking like this with bearing problems but this is my first twin cam and I'm looking for a second opinion.
Thanks

ANSWER: Do you here it at idle?
Mike

---------- FOLLOW-UP ----------

QUESTION: Thanks for your reply.
No.  It only becomes apparent when the engine is under a load.  Starting at low rpms  from a stop in first it happens briefly until the rpms increase.  Or in any gear when a downshift starts to become necessary.

Answer
There can be 2 things that is happening. First, your letting the RPMs drop to low and you are heaqring a piston knock. If this is whats happening it is really hard on the rod bearings. Its like hitting them with a hammer!
The other thing that can be happening is you have having a rod bearing going out. Usually, if this is the case, you would hear the knock at idle. Keep at ear to it and it gets worse its time to tear the motor down
Good luck and happy riding
Mike