Okay I have had this strange thing happen to me 4 or 5 times recently and have no idea why it happens. It doesn't happen every time but does seem to happen with some regularity.
When I made a fairly quick stop I hear noise from my primary and the bike actually down shifts without me touching the shifters. I even tried it with my foot completely off of the floorboards to be sure I wasn't bumping it and not know it. Still happened.
I had my bike in for routine service a couple of weeks ago and mentioned it to them. Of course they have this glazed over look in their eyes and no clue what to even check or look for potential problem.

I have faith that one of you guys can shed some light on what I need to do about this.

Don

 

I have had something similar happen to me: a near panic stop that doesn't lock the rear wheel generates a noise from the primary, almost like chain slap or something. This is with the clutch pulled in. I have never noticed whether it shifted down or not because during a stop like this, I am downshifting anyway. I have the stock compensator if that means anything...no idea what might cause the noise and it hass only done it once or twice.

 

Check your shifter rod. Put it in 3rd gear, and make sure the free play is the same when pushing and pulling the shifter. I had a similar issue on my FLSTCI, even getting a faint gear noise, like two gears juuuuust touching when I came to a stop. I adjusted that rod, and haven't heard or felt that clunk.

 

I have also had my '09 RK down shift, by itself, during hard braking. I look forward to hearing more replies.

 

you could have bent your shift fork or had the fork itself shift inside the transmission. The reason the noise sounds like it is coming from the primary is because the noise resonates from the trans through too the primary. I cant really say that is whats causing the noise but I have never heard of this problem before.

 

What bike are you talking about?
In any case.. I agree, check your shifter rod.

 

It's happened to me too, as described in the below quote. But I'm new the more modern motorcycles and I assumed it was the ABS brakes. I ride a 2010 FLHX by the way.

 

Bike is an '07 Ultra Classic with about 46K miles.
This phenomenon just started within the last month or so.