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Message: [QUOTE="TARM, post: 476746, member: 578"] I agree with you on this in a overall bases with turbos in general as a group. But to the 38R specifically there seems to be something specific to it outside the general traits of typical "acoustical performance" I guess if I had to coin a phase for it. If you consider that there are 38R that are as quite as the stock turbos yet many 38R are so far outside this as far as Whistle sound you would not think it was the same turbo line at all. When you then consider they are able to thru tuning or balancing able to change this. I guess it could still have something to do with wheel design and thus changing balance to modify the resonating frequency. I would say in general most would say a very mild whistle especially under heavy load or high boost is almost positive and found pleasant. But a whistle of certain volume and frequency in low load lower rpms such as those found while cruising could almost be seen as a manf defect worthy of warranty work its so annoying. LOL These loud 38r I put in the latter category. I would never run one that sounded like some in trucks I have driven or ridden in. It makes exhaust drone pleasant in comparison. It is this noise regardless of engine load that most find annoying. Its usually in the frequency range well over the 500mhz range you find typical engine and interior noise at we are use to and find acceptable. I seem to have notes from something I must have read during researching it. Have to see if I can find the papers or where I got it. I will post up what I must have put done as notes on the subject. There is basically 4 categories that turbo noises can be broken down into or what can generate them. That is what I think I was trying to put down. Never mind I actually found the tech paper I was going to reference. This may go way over some peoples heads from a simple lack of familiarity of the subject but some may find this quite interesting and possibly shed some light. [B]Turbo Charger Noise* - Development of a Methodology for the Acoustic Turbo Charger Layout[/B] [/QUOTE]