Has anyone else had this problem? My 4Runner is a 2000 SR5 4x4 with just under 100K on it...

I've started noticing it once the cold weather hit and it occasionally happens when it's cold and humid.
After starting my car when it's been sitting outside for a while I get a squealing sound that appears to be coming from the passenger side front... it almost sounds like it's somewhere in the dash area, but I can't really pin point it. The squealing doesn't occur at idle, but once I get the car moving around 10+ mph it starts to kick in and progressively gets a little louder with speed or if I lift off the gas pedal. The sound stops however when I get on the brake a little bit and then goes away when I slow to about 30 mph or less... but then if I accelerate again above 30 mph it comes back. The sound only lasts for about the first 5 minutes of driving until the car warms up and sometimes comes back if I'm driving in wet conditions.
I'm pretty sure it's not a drive belt for two reasons.
1. I just had all the drive belts replaced this past summer.
2. Normally a drive belt would squeal whenever you step on the gas pedal and continue at idle.
I've heard something about a "squeaky fan" but haven't really heard or found anything on how to fix it... if that's even the problem to begin with.
Does anyone have any ideas what this may be???

Thanks in advance for the help.