97 civic ex air intake humming sound at idle
 

Hello fellow Honda fans I am having a problem with my 97 civic ex, It seems there is a low humming sound coming from the air intake. The sound gets louder when I take off the cover like you would to replace the filter ( I have the stock air box ). Anyhow it does this when the car is idling around 800rpms. Does anyone have any idea what this could be? There are no other problems other than the noise but I am really scratching my head at what this is. :confused:

I know its not the radiator fan or anything silly like that.
I just replaced the PCV valve but i doubt that has anything to do with it, plus it only goes in one way.. so..

Any help would be greatly appreciated

With out hearing it ,it's hard to say,if the filter needs replacing that could be the problem but you say it does it without the filter in the intake box,I'm just guessing here but buy a can of throttle body cleaner and soak it let sit then crank it and spray it while it's running,maybe it's just dirty,sorry we couldn't be more help.