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Hi Folks. Wondering if anyone has heard anything like this before. Head is a RB25DETNeo and this tapping happens just for a minute or two after starting Hot OR Cold. There are no unusual sounds otherwise. It sounds to me that it's similar to a SR20DET VCT rattle, however while this sounds like it is in the same area, it happens if the VCT solenoid is unplugged. I don't know if this will actually affect things, if the issue is internally mechanical and not solenoid. There's not a lot of info on VCT rattle on RB25DET's. I have blocked off one oil feed to the head to combat blowby in the past. Note: This happens at about ~1500-2000 rpm. It will rattle once, or twice, and the car can rev past it fine. I.e, if you revved to 4k you may hear 1-2 taps while it revs through, but it always appears at that range. Note: If you rev the car slowly through the rev range after starting, this does not happen. You don't need a ton of throttle, but if you stab it or stand on it it'll happen, it will not happen if you say hold throttle at 10% and slowly rev through the range. The sound appears to be coming from the intake cam, from what seems to be just under the throttle body. Again, hot or cold, doesn't matter. Will hear it for about a minute of driving and it'll fade away pretty quick. Leaving the car idling does help if you leave it idle for ~2 minutes etc. No weird sounds under load at all. Car otherwise drives fine. From what I can tell, if you leave the car sitting for maybe 5? minutes, the sound will return on re-start. A little less than it would if the car is left overnight, but not much. Could be related (maybe not) but VCT has only just actually been switched on/wired in recently. Could be piston slap. Could be wrong oil, (5-40, was 10-60 in the past) could be something else entirely. Sound does not appear to be getting any worse since I noticed it (couple of weeks). May have always been there, because the car was previously auto and any throttle will go well over 3k RPM where there's no sound and no load. Any hints as to what this could actually be given the above info? Looking to know where to begin, or whether to begin at all if this is actually a common thing people don't talk about.
