Strange noise coming from '99 Cat

[moerome]

Hey folks, hoping you can help me out here being a newbie on this forum. I have a '99 Cat that is making a strange noise that sounds like something is blocked. It appears that it's coming from the duct that is between the defrost buttons and mode button on the AC/heater console.

This noise occurs when I'm "cruising" on the highway. When I reach 85mph, that's when the noise kicks in. It's becoming quite annoying.

Wondering if anyone can shed some light on the probable cause. Thanks.

[moerome]

A little more clarification on the noise.......it sounds like a cross between a whistle and a blocked air vent. That's about as best as I can describe it. I may take it out on the highway again, get it up to speed and try to record it and post it for you to hear. Thanks.

[Marks DTM Calib]

Possibly the climate control air sampling fan getting noisey......I assume the cabin vents in the passenger side rear boot are clear (open the trunk and look in the cubby hole on the right....)

[moerome]

Marks DTM Calib:

Per your instructions, there was this plastic cover "thingy" that was leaning up against what appeared to be vents (I assume the cabin vents you had referred). I'll take her out on highway to see if the noise continues. Good lookin' out!!!

[moerome]

Hey Marks DTM Calib:

Well, took the '99 Cat out on the highway this afternoon/evening. Cranked it up to 90 mph, and guess what? No noise!!!!

However, upon returning back to town, I was cruising at about 70 mph when this 5 series Bimmer shot by. So, I said, what the heck and jump in behind him. We had it going for a while between 85 - 100 mph.............and the noise returned!! Even when I backed down to 70 mph letting the Bimmer go on about its business, the noise was not as bad, but intermittent.

You made mention of the climate control air sampling fan. Where is that guy located, and how difficult would it be for me to replace it myself if necessary?