New Engine Rattle- Sign of Tappet Failure?

Rode without earplugs today and while blowing the socks off a stoplight revving joker on a Harley I noticed an engine rattle I haven't heard before. It happens at high revs when I abruptly open the throttle. It lasts for about one second and then it's gone. It's a very harsh rattle-can noise. I got it to do it a few more times in different gears, but it's hard to tell if it's coming from one side or both.
It may be that I just haven't heard it before because I usually wear earplugs. The rest of the time the engine sounds great.

Wondering if this is the first sign of trouble from my flat tappets?  

What other warning signs should I be listening for?  I would imagine more rattles that don't go away or get worse?

Could be pinging/detonation etc.
Is your bike 'Beetle' mapped?

Yes, freshly mapped with Beetle's factory can map and she's running beautifully in all other respects.

Sounds like it might be pinging. How's your TB balance? Poor balance can cause pinging.

Thanks guys! I'll check the TB balance ASAP.

Sure it wasn't the Harley??
Wait!! High revs you say? I guess it ain't the hog then.

Also, when you did the map upload, did you reset the TPS and self learning parameters? If not, do so.

Sounds like detonation to me. Usually this is worst at low rpm, wide throttle but it can occur at any time if the mixture is too lean or the spark is too advanced for the fuel's octane rating.

Pete