my engine makes vibrating noise @ 4k rpm

[240meowth]

ok, it's been bothering me for quite some time now, eveytime i'm on the freeway, or going fast.  once my engine hits around 4k rpm, it makes a rattleing noise or humming, or vibrating noise from the engine bay, since i'm inside the car, i have no idea where it is.  it's towards the center of the engine bay, is it the exhaust heat sheild that's rattling?  or what?

[240sxspeedracer1]

yeah, it could be heat sheild, or it could be that maybe u hit the exhaust on the curb and messed it up.
I bring that last one up cause it happened to me and now i hear that #### rattling noise.  
tell the muffler shop to check it out and have them fix the heat shield or take it out, i took my heat shield out cause at first i thought that was the noise but it wasnt.  the point is, i fell no differnce in heat or anything.  Its not like the carpet is melting or something so dont worry about that.

[240meowth]

if you take out the heat sheild, does it increase your underhood temp? 'cause i'm thinking about taking out the mechanic fan. and i have to be causious about the temp under the hood

[chickenmanq]

Look for loose sheet metal.

[sykikchimp]

I took the heat sheild off my old 240, and it started messing up the liner on the hood.  I guess it was singing it or something.  It just started getting torn up.

I had a 90.

[SlowS14]

If you ahve an aftermarket header that could be it.I have a Greddy header and the bolts are always backing out.When loose I get a horrible sheetmetal sounding vibration.