Some of my a/c have a kind of "sound coming down a hollow tube " effect - I recall that when I purchased the Dreamfleet C310 , it had this and they issued a new sound file that fixed the problem.Does anybody know what causes this?Thanks Barry

Barry, I don't know the cause but I'm familiar with the fix for the 310. I used it for sometime until one day I cut one of the engines and lost all engine sound. I went back to the original sound that had the "hollow tube" effect.Since the fix only seemed to be using one engine sound I surmised that the problem had to do with the stereo phonics of the sound file. The fix had the twin engine sound at start up but seemed to switch to only one engine sound after that. I don't know why, other twins don't have the problem.