strange noise from front of motor at around 2800 rpm

[poorsche1]

well i am back. been on a project that has taken most of my time and any free time i had, was spent with the family. so i had not been able to work on the porsche. but now project is over and i am back in town and have been able to work on the Boxster. i changed the tensioners and yes the one under the AC was a pain and the result is that the sound is still there at 2800 RPM. a porsche mechanic came buy and told me that i had a bad vario cam guide or more that likely a broken valve spring. well tore it down yesterday and guides look good and springs look good. now the mechanic sais he is stumped could have sworn that i had a broken valve spring.
there are no codes in the computer
vario cam stuff look good
valve springs look good
tensioners are new
LN engineering IMS bearing
Idle is perfect
what else could cause a clatering sound at 2800 rpm
can it be a bad lifter how to test the lifters?
had a friend tell me it could be the flywheel. can a bad flywheel make clatering sounds that only start at about 2800 rpm
i am now stumped
any ideas guys
wife and the kids are out of the country on vacation for a few more weeks, i had planned on using my vacation time from them to change a broken valve spring. glad it wasn't a broken spring but what the hell is making that noise?.

the S has 41 000 miles on it i don't track it, drive it mostly normal, every now and then race some kid at the light but i paid for the car so i don't drive it like i stole it. I drive my v6 accord like i stole it most of the time and that stupid thing has 215,000 miles on it and the only thing i have changed on that is the oil and the timing belt. Porsche builds a great car but they need to take some seriouse quality lessons from the guys at Honda and Toyota.

[Jager]

Is there clattering noise above 2800 RPM?

[poorsche1]

yes the clattering starts at 2800 rpm. i didn't rev it to 6grand but as you give it more gas it climbs with the rpm. the sound is not a super loud pots and pans clatering or the sound of a spun bearing or broken rod, which i personally remember what those sounded like from my 914. but as you hit 2800 you hear a steel on steel rattle comming from the pasenger side. sound is there with no belt on so that eliminates all the usual culprits

[Jager]

Might be a lifter? I don't know how to test those, I end-up replacing all of them. Could it be an exhaust leak? Those can sound like metal hitting metal sometimes and have messed with my head. It would be in the area where the manifold/header bolts to the head.

[poorsche1]

did you have the same problem?

[Jager]

Not on my Boxster but other vehicles.

[poorsche1]

what eneded up being the cause?
you are saying exhaust might have something to do?

[Jager]

I have had exhaust leaks that sound like lifter or valve noises. The problem ended up being loose manifold/header bolts or bad manifold/header gaskets.

[poorsche1]

i will look for tell tale signs of exhaust leaks

[poorsche1]

update on this issue. no more clatering at 2800 solved that issue created another. i have not had much time to work on the boxster for a while, but i had taken the apart the valve cover on bank 1,2,3 a couple of months ago and found what i took to be 4 colapsed lifters (tappets), 3 exhausts and 1 intake. I purchased a new set for that whole side, last week i had time to dedicate to reassembly, put it all back together it started once in the beginning and for two days after couldn't get that thing to start for nothing. it would shake and sputter and pop but would not start. by that time spark plugs were fouled, changed plugs tried again a few more times, nothing. next day checked plugs, they were fine, tried again until it started but it would backfire and pop for about a minute then it leveled off and sounded good but when i take my foot off the gas it would die. drained fuel put new fuel in (fuel had been in since february) checked timing again, timing is on on both sides, removed MAF cleaned it put it back in it starts, sounds good at 1000 rpm and above, take foot off gas and rpms dive and motor shakes and sputters, if i slowly give it gas it will pop or backfire and then levels off above 1000 rpm. code reader keeps giving me P0300 P0306,305,304, cleared them a few times but the reader pick them back up a minute or so after i start. swapped the coils to other side, recleaned MAF still get the same P0300 for bank 4,5,6, and the check engine light comes on and starts to flash
anybody have any thoughts as to what it might be? the misfires are from the side i did not work on.