the chatter sound comes from running no recirculating or blow off valve
the pressure builds up behind the turbo and as the throttle is closed the pressure can only get out through the turbo inlet which is still spinning which causes the chattering noise that is heard as the pressure exits out past the compressor wheel.
Not sure if there are any real negatives on low boost that would effect the turbo's longevity but i'm sure that on higher boost setups of well over the standard turbos boost capabilities then this would not be too good. This setup will also give slightly more lag when accelerating as the pressure is forcing the compressor wheel to spin the other way which slows it down, but with the turbine wheel still receiving exhaust flow perhaps this effect may be negligible.
positives are that it sounds cool.
none of the above is based on fact, i'm an engineering student and thats how i see it. open to correction.
There's a lot of scary posts on the Internet as to whether turbo chatter/flutter/surge is actually damaging the turbo. If I gently spool the turbo off WOT to 0.3 bar at around 5,000rpm, I get quite a distinctive chatter. My screamer pipes then make an even cooler sound once the wastegate is opened!
I'd be interested to see what people feel about turbo chatter/flutter and whether it is truly dangerous. I'm not sure I'd like to hear the chatter at WOT at 8,000rpm though as I think that might actually put stress on the turbo if the air were being forced back through the compressor housing.
I've run bb turbos without bovs for a long time without anything happening.
And I've yet to see a log comparing the same setting with and without a bov. I doubt there's any noticeable performance difference.
Although I do believe the turbos life benefit from not having the air stopping the impeller but they won't die in a couple of hundreds miles...
Wastegate chatter is fine and is simply the valve cycling.However the fluttering sound that comes with surge from the intake is not good! The real killer is when you hear a small pop from the intake when lifting.this is the blade tips exceeding the speed of sound,and the resulting shock wave kills all but the biggest turbos.If you insist on having no dump valve,then at least get an over pressure valve(bov),and set it to just above your boost level.
There was a article on Autospeed about this some time ago. Running no BOV puts a large load on the turbo. The BOV reduces this load. I have a memory that perfomance was better without BOV that not much better (tiny fractions of a second).
When I asked a guy a Prodrive about BOVs he said that they didn't use them ebcause they were keeping the turbo spinning with anti-lag and such like. He also mentioned that turbo lifespan wasn't an issue for them.