It seems to me it's the typical "shaft-drive slack" from wheel turning and shaft itself on crownwheel. Basically engine accelerates rear wheel then it sits on one side of the tooth, till it catches up and hits the other side of the tooth (as much there is room between the crownwheel's teeth). I have the same noise on R1100GS running it on centerstand with rear wheel up. Running on constant idle revs seems to be the worst irregular sound when in gear and rear wheel spinning freely.

If any of the gearbox bearing are worn you should hear real mechanical grinding noise - like someone has put a low revving coffeebean grinder machine into your gearbox and drowned it into a thick oil (height of the sound is what revs you are riding at, on neutral gear revving you usually hear nothing (with the only exeption when on input shaft bearings are worn, which is 1 of the 3 rotating shafts) it my case it was the intermediate shaft's bearing which I could only hear the best when I was riding or revving it on centerstand in gear - but as said, a confusing factor can be the irregular noises coming from the shaft drive slack from a free wheel rotating w/o road contact). But yes, on boxer and old K- BMs with separate ("exposed") gearboxes - worn bearing sound is VERY distinct, well audible and hard to miss even when riding in the wind noise. I rode couple of hundred kms slowly with that loud worn bearing noise no problems to get a workshop and repair it in Australia. Thankfully local bearing shop had the same type/size bearing in stock (and another funny thing, when I opened the box on a "Made in Germany" bike, the prematurely broken bearing was, ironically, the stereotypically "Made in Japan" stereotypically known to be ultra-high reliability quality products ). And it gets even better, the same Japanese (NTN) company makes the same bearings in Taiwan now, so I had to use Taiwanese one to get me on the road again Talk about globalization.

Anyways, if you don't hear any threathening sound from the gearbox you're just fine and ride on.

And don't worry too much about the bike - LOTS to see in Indonesia!

Ride safe, Margus