carrrnuttt

Well, it sounds like it anyhow.

It only occurs (at least the only time I hear it) when I back off the gas at about 3K-4K RPM with the clutch still engaged. Essentially, engine-braking. It also only occurs when the engine is cold. As in, I have a ten-minute drive to the freeway onramp, and a 40-minute cruise from there to my work exit. By the time I exit the freeway, the "sewing machine" has apparently dropped off from my engine. The same pattern occurs in reverse, coming home. This has only been noticeable since nighttime temps started getting into the 40's and 50's here, where I am.

Any thoughts on this? I only use 91-octane on my car, and all my internals are stock, and timing is as well. The only mods directly attached to the motor itself are: VIAS delete block plate, short-ram intake, OBX headers, custom exhaust, and not sure if this is necessarily a "mod," but it is attached to the motor, and it's not stock, and that is a 6-speed HLSD transmission from a 6th-gen. The sound itself is as described: an old school sewing machine going full tilt. A very mechanical, steady noise. It's either a rotating noise, or a very fast vibration. It does NOT happen when I back off the gas and the transmission is not engaged.