I have recently bought my first bike, a gas gas txt Pro 125 06. 

It seems to be making a knocking noise when running as can be heard in the video. This is filmed straight after it has been started from cold. 

I have seen other videos of bikes making a similar noise so was just wondering if it is worth worrying about? 

Cheers, 

Joe 

https://youtu.be/VtRyl_wjqwM

 Pulling in the clutch will remove some of it. Should sound pretty normal riding around.

@lineaway okay cheers! Was concerned it was piston slap or something like that

It should go a lot quieter with the clutch pulled in,does it?

@huski I tried it this evening and it didn't seem to, just stayed the same 

Gearbox oil....check or replace...read replace with correct grade/ viscosity. Otherwise like other members have stated....sounds ok. Try clutch in and in gear that may take some noise away. Listen to other trials two strokes some make a hell of a racket yet are perfectly ok.

@section swept Apparently it had the gearbox oil done just before I bought it but I'll check anyway, cheers! Clutch in and when in gear seems to make the same noise. Was just concerned because it sounds more like its coming from the cylinder area and I'm not too familiar with 2 stroke engines

Thanks for the reply! 

Take clutch cover off and look closely at the teeth on the primary gear and those on the clutch basket. You can get some grit in there or wear on the teeth and it can result in a sound like that.  Any fuzz/metal on the drain plug magnet? 

@mbeers6 I'll have a look over the weekend, thanks! 

While you’ve got the clutch cover off, check the round kick start idler gear which sits behind the clutch basket.

They get damaged, and need to be replaced fairly frequently. A damaged gear can make a noise similar to your bike. There will probably be more swarf on the filler plug magnet than the drain plug magnet.

Failing that, it could well be the small end bearing.