Strange /Weird Noise during acceleration
 

Hi
First post on tech side and new to 370z and S/C. Have been doing a number of searches on the forum but could not find something replicating the issue I have.

I'm hearing a strange noise coming from the front of the engine, but only during acceleration and only between ~2500 and ~3100 rpm. On deceleration there is no noise, unless you ease of the gas slowly - then it may or may not appear. It is more distinct when you open up the gas slowly or cruising with your foot lightly on the gas in that rev range. When you gun it, the revs pick up quickly so if audible it would be for a split second.

Very difficult to describe the noise: Its a low pitched screeching / chattering sound. (Very much like a shuddering noise - as if a clutch is lightly engaging - but in this case the noise comes from the front. It's not very loud (therefore no sound clip possible) but my exhaust is.)

Under normal Idle and under revving in neutral the engine, S/C, belts and pulleys are absolutely fine, this noise is also gone. All silky smooth. BOV seems fine as well.

Car pulls fine and I had a local tuner and tech from Nissan drive the car and they feel nothing is wrong with the car, but could not say what the noise was.

The car has a K&N filter system GTM S/C Kit and Rotrex C38 S/C. De-cat exhaust, which is really noisy and droning. The previous owner knows about the noise and he lived with it for 3 years and about 18 000 km's - he put it down to the Rotrex planetary gear ramp-up stage - I'm not so sure as the local Rotrex agent said these blowers are really quiet.

If I look at other options based on forum search the following may be possibilities:


- Air-rushing noise through the K&N set-up / vacuum?
- Throttle body noise <25% open?
- Dual-mass flywheel - resonance noise at that frequency?
- S/C busy going?
- VVT - related and kicking at that rev range?
- Pre-engagement of VVT?
- Catless down pipes resonating at that range?
- The belt tension and pulley system?
- Timing chain and tensioner system?


Why is it an issue for me? If it's normal I'll learn to live with it, but if it can be fixed or it's an indicator of something failing I would like to have it sorted.

Would appreciate any ideas or experiences.

Is the noise a chattering or fluttering noise? The bypass valve chatters on my system. about 2500 to 3000 rpm under modest acceleration. I have used 4 different by pass valves with the same result. Different BPV springs, tightening the spring rate, loosening .. nothing works... annoying as hell.

ck. the oil in the SC,if it's a stand alone lube system....may need changing.