mk2 1.8 subtle vibration @ 3500rpm

[Simbu]

It's subtle and doesn't seem to affect the performance of the car... but it is there and feels like a slight vibration through the accelerator pedal. A few hundred rpm above or below and it disappears. It's a bit annoying since the gearing puts 3500rpm in 5th at 70mph... I find myself keeping it above (or below) those revs when cruising; now i know its there, it's annoying!

Does anyone else have this?

Maybe i'm going a bit mad

[tuttle]

Assuming its rev specific not speed, ie your wheels are all round & weighted correctly etc.
I think there is a fairly common resonance thing that goes on with mk1s somewhere between 3k-3.5k revs. Usually its just a heat shield. Mine used to make worrying vibrations at exactly 3.2k revs which i could feel through transmission tunnel & stick, turned out to just be heat shield vibration. It would be my 1st place to start checking before I started worrying about more serious issues.

[MX-5 Lazza]

As above, do you get this in all gears at 3500 or only in 5th?

[Simbu]

As far as i can tell, it's all gears. It does feel like a resonance, rather than something 'wrong' with how the car is performing, if that makes sense?

I did replace a bolt on the exhaust manifold heatshield a while ago, but given this something i can feel up the accelerator pedal this seems unlikely to be the source?

I will check when i get home though.