VF500F engine ticking sound (not worn camshafts, camchain etc...)

Hi folks,

Could anyone with V4 experience please listen this ticking sound on video clip below and have idea what it could be? Engine is working on idle speed (cca 1500rpm). From 0 to 13 sec, there is no any ticking. Than I pull throttle a little bit (to about 1700-2000 rpm) just to provoke this sound and you can here distinctive ticking from 13-28 sec. Than it stops and come again from 32-38 sec. After 38 sec of video there is no ticking anymore...

[video=youtube;skgQroajqPA]http://www.youtube.com/watch?v=skgQroajqPA[/video]

Now, camshafts are in great condition, camchain and camchain tensioners also, valve clearances are checked... Carburetors are not yet properly sinchronized (is this could be an issue?!?).

What else should I check? I think that ticking is coming somewhere from rear left side of engine, but I could be wrong... Also, this ticking do not affect driving. There is no any strange vibration, no power loose, no smoke, no temperature rising etc...