Fuel, Performance and Buzzing Noise

[Renox]

Hi all,

May sound like a very stupid question to ask but if the fuel level is low would the ECU detect this and reduce performance?

There seems to be way less punch when at a quarter or less of a tank (very rarely hit this mark).

Also when starting the car from cold you get like an electric buzz for 4/5 seconds which clears instantly does anyone know what this is? No issue with the engine or car just curious what the noise is.

Thanks,

Renox