Rattling/ticking noise @3,5-4,5k rpm after 20-30 min drive + video

[Bax]

Hello everyone,

First of all I have check many threads about engine sounds, and I am only creating a new one because,
in other threads the sound is completely different, usefully people have knocking sound in the engine.
Which is not the problem in my case.

When does the bad sounds starts?

First I start my bike, and warm it up with choke for about 3-4 minutes. Everything is fine at this moment.
When engine is warm I start to drive and there is no problem for about 20-30 minutes.
After about 20-30 minutes Rattling/ticking noise starts. And it will continue for the rest of trip.

When I hear Rattling/ticking noise?

At around 3,5k- 5k rpm when slowly accelerating you can hear this sound, but it becomes much launder
when I release throttle and rpm is falling. You will be able to see it in my video. I think it makes this sound at higher
rpms as well, however it is harder to hear and I haven't driven my gs more than 8k rpm

When the sound goes away

It varies, one time once the sound started it was there all day, only next morning it was gone again for 30 min, however when I was recording this video. I drove back home, went to change clothes and a take dslr camera to make a video with better sound quality.
It took me around 3-4 minutes when I started the bike the sound was gone, you will see it at the end of a video. Another time i went to get gas after I was done I started the bike and the sound was gone for some time.

My bike year 1989, miles 49 709, could you please advise me what could be the problem.

[prmas]

It is always difficult to identify sounds from a video clip but it might be cam chain. It certainly sounds to me like top-end noise.
How is engine performance? It seemed that engine response might have been a bit slow when you blipped the throttle. It does not sound crisp. 

Macka