M20 High RPM rattle

[Sagaris]

When accelerating I notice what sounds like a sheetmetal exhaust shield rattling when I am above 6200 rpm. Normally I would suspect the heat shielding on the cat. converter having a broken weld or something but in this case the noise seems to come from the engine as if it is in the cylinder head. The only thing that has changed since I started noticing the noise is a 5spd swap.
If it is exhaust resonance related then either my cat. is coming apart inside and causing the noise, or the fact that I do not have an exhaust hanger is causing some strange harmonics due to not having that support point.

If it is engine related then I am guessing that something in the cylinder head is rattling. I am just not sure what.

I have heard this same noise on other M20's at high rpm.
Any thoughts or ideas?

[SmokeE30]

try posting a video but if it sounds like its in the head pop the valve cover off and check to make sure every things in place under there. the only sheet metal thing you would have messed with during a 5 speed swap would be the sheet metal plated between the engine and transmission bell housing did you remember the 10mm bolt that holds it on the passenger side?

[5Toes]

I might have the same noise, but I would describe mine as "valve float"

[Sagaris]

try posting a video but if it sounds like its in the head pop the valve cover off and check to make sure every things in place under there. the only sheet metal thing you would have messed with during a 5 speed swap would be the sheet metal plated between the engine and transmission bell housing did you remember the 10mm bolt that holds it on the passenger side?

Good call on that 10mm bolt. Something to double-check.