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[bambleweeny57]

I hope this rings a bell with someone, because it's driving me nuts!

For a couple of weeks now, I've noticed a rapid crackling/clicking noise feeding through into the cabin while accelerating. It sounds almost like a gurgling sound or a muffled solenoid rapidly clicking. The noise occurs ONLY while accelerating, and ONLY in 5th (between 3000-3600 revs or 65-80mph). If I take my foot off the gas at any point, the noise ceases. If I change down to 4th, the noise disappears INSTANTLY(at the same revs and speeds) and only returns a few minutes after returning to 5th. I cannot get the noise in any othr gear at any other speed or any steady speed. It seems to be only related to engine load & acceleration. The noise typically takes about 10/20 minutes of steady freeway driving to start, but once started it's fairly persistent. It becomes more rapid/loud as the acceleration spurt progresses, until passing 80, when it vanishes.

I cannot pin it's location down at all, it just seems to emanate generally from the forward compartment, as if the dash is just acting as a sounding board feeding it into the cabin from where-ever it is.

I have an FCX-II code reader. I have no diagnostic warnings at the present, but several weeks ago just before this noise started I did get a "functional check purge valve" and a cylinder misfire warning. I cleared them to see if they would recur but so far they have not. This purge valve (13-90-1-433-603), was only (supposedly) replaced three months ago by my dealer.

Most recently I've noticed a slight high pitched whine accompanying the acceleration (increasing in pitch as the spurt progresses/speed increases). it seemingly comes from from beneath the cabin floor. Sounds like a pump struggling to me, but I'm no mechanic.

If anyones has clues as to what this could be or how to diagnose it further, that's be fantastic. I know the car's trying to tell me something, I'm just to dumb to understand.

Cheers
Paul

P.S.
My first thought, given the almost gurgling quality of the noise was A/C. It really does sound like a fluid/gas system reacting to a pressure increase by leaking/bleeding. So I tried every AC/fan related thing I could think of. Turned it off/on, fan low/high, recirculation on/off, temp up/down. It had no discernable effect on the noise, immediate or long term. It really does sound like stuff I've heard from an A/C before, I just can't explain the very strong gear/acceleration correlation or lack of A/C function correlation.