Sounds like electric fan but is not...?

Noticed this after a long highway ride, the fan is not on but it will sound almost like a low fan setting, as soon as I heard it I was thinking fuel pump, It only does it after the bike has warmed up and not every time. I know there's the spinning water pump impeller that could also be making this noise, but the bike runs like normal and holds fluids (of the correct color..) good. Anybody have this symptom right before a breakdown? Btw it's an '08 R with 2500 miles and every HP mod done short of the 290 kit.

Mine did that. The fan blades came loose from the fan motor shaft so when the fan came on it just made a humming sound. I had to buy a new fan/motor assembly. My bike had been crashed and the fan blade was contacting the radiator.

My fan did that too but I was able to glue the blade back onto it.

It doesnt take much to strip the fan blade on the motor, I droped the bike in sand which didnt hurt a thing execpt the fan.

Never dropped... Not the fan, I think it was corrosion in the water system causing the impeller to make noise, rode it long and hard today with the new coolant, seems to have gone away for now...