Sound from dashboard area

Anybody ever had what sounds like a muted static-y sound coming from the dash in their truck? Seems to change pitch with the motor rpm. Also sounds very similar to the fan for the defrost except I hear it even when it's off. Starting to wonder if it might be some seal/grommet that has come loose and is allowing more sound from the engine bay into the cabin? Whatever it is it's driving me nuts. Any ideas on what I might look for? My truck is a '02 base 2wd single cab with a 5 spd.

 

Check the rubber seal at the base of the steering column where it passes through the firewall.

 

Is it coming from where the windshield meets the dash? If so, get some weatherstripping, the stuff you would use on doors and windows in a house, and stuff it down in there.