No, its' not a snake. When I drive 70+ mph, especially in a headwind, I have a rattling sound coming from the passenger side dash area. I thought it was a bad fitting filter, but now that I'm on my third, different brands, I still have the noise. My wife's Cobalt does not. I keep forgetting to ask the service advisor(s), or my friend with a HHR, but here's my chance. I've searched the forum and not found a reference. My '04 Silverado makes a similar noise, but it's from the outside trim and a known problem (and fix), and not as frequent. But the HHR rattle sounds like it's internal. Anyone else have it?

 

Wiper arm loose? Checked the front passanger wheel well liner-are all the plastic puch pins in place? May not be in the dash...

 

A longshot but check your roof antenna to make sure it's tight. The noise can sound like it's in the dash area from the driver position.

 

I have checked all front (and rear) end pieces, hardware, and fasteners in the last two weeks while doing brakes , shocks, tires, wheels, and tow straps. Nothing amiss. I checked and changed wiper blades the previous week. Up to spec. I am thinking about removing the cabin air filter to see if there's a difference. Another thought... could it be the engine air filter assembly? I doubt it, since at lower road speeds, but at full throttle, there is no rattle. Also: just went out to check antenna. Tight!?!

 

You MIGHT have a reasonable idea with the air filter box. If I remember correctly a couple of owners had broken or lose brackets.

At higher speeds it make be pushed back and "resting" properly. You probably did this but I would check to assure everything is tight in that area on the passenger firewall.

 

how about that butyl patch? could be flapping in the wind.

 

Also check the fender liner on that corner, had the one on my '07 left loose by the dealer and that rattle drove me nuts for a week until I stumbled onto the problem after much tinkering and looking.

 

I'm amazed at how many Plastic Push Pins are not tight as I go around looking under fender wheel wells etc. etc.
Many Plastic panels and such are just plain loose and some can create excess noise when bumped, hit a hard chuck hole or bump, or under high wind conditions ... like buffeting @ 60/70mph.

 

Those little push pins are so cheap that when I had the bumper off to change the headlight bulbs I just replaced all of them, no more rattles and things are nice and super tight. Sometimes I yearn for the days when things were fastened on with good old fashioned nuts and bolts.

 

There is a known noise that comes from the passenger side of the dashboard. There is a technical service bulletin for this which includes fixes. Dealer fixed mine, among other rattles, for $600 of labor. Car had to go back (twice, at no additional cost) to redo fixes for two other rattles, but the dashboard one was fixed on the first try.