Recently, when i'm driving in the morning with the engine still cold...

at about 4-5k rpm, the engine makes a raspy metallic noise.

for example, from idle and accelerating, you hear the normal rev noise...then while continuing to rev higher, at 4k rpm, the rev noise turns into a metallic vibration.

obviously i stop revving so high and the noise is not there.

then when the car is fully warmed up, the noise is entirely gone.

my question is, since i never had this noise for the first 90,000 miles...what is it?

i know it's related to a cold engine...but is it a sign of something going out or being loose?

 

Isn't your motor FI'ed?

 

What engine oil do you use? Have you recently switched?

 

Could be a number of things. Start with the simple bidness. Check heatshields, or other thin, rattly metal parts.

Have you ever had a valve adjustment done? Could be that.

Could be an header/exhaust manifold crack starting. Could be a loose header/exhaust manifold.

Premature signs of another exhaust leak maybe further down stream.

Have you done a visual check? Just pop your hood and start kinda tapping stuff with your palms or fist and see if it rattles (with the car cold). Then get underneath the car and repeat that procedure.

 

stock motor, k&n fipk pipe with oem filter.

 

i use amsoil...been using amsoil for the past 80,000 miles.

this noise is new. but always happens with a cold engine at above and around 4K rpm.

 

that's a lot of options you mentioned...however, i can eliminate MANY of those options due to the fact that this only occurs on a cold engine, for example, first thing in the morning.

and, it happens above a certain rpm, around 4-5K rpm.

the pitch is rpm related, meaning it correlates with the higher pitch engine noise at higher rpm...it's just that the engine pitch noise becomes metallic rasping at 4Kish rpm.

when the engine is warm...the noise completely goes away at all rpm range.

i will take apart the exhaust mani and header to see if i notice anything there.

anyone know what it could be?

i'm guessing timing chain or something internal doesn't like the cold temperature...being my engine is now at grampa age.

 

I'll bet on an exhaust heat shield. Especially since it happened after many miles (rust/deterioration) and only when cold (small opening now but it'll get worse with time/deterioration). You may only have to bend something slightly to keep it from happening. Happens on many cars...

 

Lose an oil cap lately?

 

no.

loose/lost oil cap does not even come close to my description of the issue, but thanks.