I've done a search on this and didn't find anything really close so I'll ask the question.

I drive 19 miles to work one way everyday on a freeway. I cruise at 80 mph and I've noticed that when I exit the freeway and drive on surface streets my intake makes really loud, raspy intake noises when I accelerate from a stop.

If I get on it, it gets really loud at 5,000 rpm's and you can feel the engine loose some power. The strange thing is it did this last winter and then ceased once the temps rose above 50 degrees. Now the temps are back in the 20's & 30's and the noise is back.

If I let the car sit for a while and then drive it again, it's fine. For anyone who owned a Ford Taurus SHO, it sounds just like it did when the plenums opened up under hard acceleration at 4,000 rpm's.

 

I believe...but dont shoot me if i'm wrong, that what you are hearing is your butterfly valve opening up into a full ram air intake, which IIRC, is at about 4,500 RPMs. That rasp is just it sucking in air.

 

The strange thing is, my intake is affected by constant speed. If I drive my car in 25 degree weather around town, I can and have floored it and the intake sounds fine.

If I drive at a sustained speed for a while, then floor it, it sounds like my intake is about to explode. It's really strange.

I forgot to mention I have a drop in K&N filter.

 

You might need to clean it. (Filter)

Or read the directions about oil use on it. I have no clue because I haven't owned an intake with a filter requiring oi, but I'd check to make sure it's done properly, and clean.
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BLCKPOIZEN

 

It's clean and oiled properly. I've been using them for years.

One other symptom is this: This morning on the freeway when the noise started, I had the car in sixth gear cruising at 80 and when I hit the accelerator, the noise grew louder but the car would not accelerate. The tach never moved off the 4,000 rpm mark.

 

Ah, the 'ol SHO...I almost miss her. I had a '94 MT SHO before I got my 8. I loved that sound as the secondary intake runners open up at 4k. Fabulous engine that Yamaha is. If I could put that 3.0L Yamaha in my 8 I just might do it!
If your intake sounds like that, I might just roll with it (but if your losing power than thats a diff. story)

 

I do believe sound travels differently when cold, in fact it's more pronounced and you can hear better. Also there is a differance in pressure. More pressure from cold air will make a different sound.

Your KN filter will be louder than stock.

The noise you hear is normal.