If that made any sense... its really difficult to explane..

 

If I got it right, I still would put my money on wheel bearings. Ask your bf to hold the bike up, and try to wiggle the rear wheel sideways and look for slack (feels like the wheel has a tiny bit of room to move. If you can, drop the chain from the sprocket and spin the wheel freely as fast as you can with your hands. If the bearings make this hollow rolling/humming noise they`re due for change. Pretty easy job to do yourself, just don`t get the new ones from a bike shop and pay yourself silly, If the bearings prove to be the cause, I could try to get new ones here, got a few shops like Laakerikeskus and Jokilaakeri where I could get them for a fraction of the price if they are regular sized.

 

humm... but if they are bearings shouldnt they make noise also when I am on move and engine is off? I mean they should make noise on moving...and after I come to a stop in cross section start giving a little gas and go up to 40 km per hour I can hear the noise.. And I tried on giving a little gas so that it would run around 30 40 km per hour and hitted the red stop... Noise dissapears.. can only hear the wheels go around and a bit the chain... but when turning it on again and giving gas again the noise comes back... shouldnt I hear them in the moving motion?
And thats on the road...

 

It might be something else, but sometimes a bearing going but not yet all gone makes noise only when you put the most torque through it, as in the little gears. Sometimes a little piece of the surface material on the bearing track comes off and causes a trrrrrrr-like sound when in slow speed and levels out when you go faster. Just a thought and something to test, can`t say for sure. You say turning the engine off makes the sound disappear? It MIGHT be because of the stress is relieved from the bearing, OR it might still be a bearing, but in a different place like the clutch. Just guessing cause I can`t get there to test it...

 

well we tried that and theres no slack there.. alls fine...in the back bearing.. tight as it should ´be..

 

So it`s prolly sumn` else then... Sorry, no help...

 

chain and back tire - YouTube

Not a glimpse of the noise i am complaning about (

 

Maybe an optical illusion but is that chain tight that would cause some noise.

 

ou its tight allright...

 

Don't make it too tight. They need slack, and just the right amount. They get tighter as the suspension compresses from the weight of the rider and movement from the road.