Reduce EMI generated by old AC motor from an electric knife
Sounds like you have low frequency conducted EMI. An X-capacitor straight over the motor would be the first order of business, but I've included the steps I would have taken down the line (litterally).







simulate this circuit &ndash; Schematic created using CircuitLab

Couldn't find a symbol for you motor, nor lines to draw a correct CM choke.

More luck with LTspice:


All values are estimations, but at least not several orders of magnitude off.

To be compliant, your capacitor needs to be at least X2-rated. The R in parallel would be required in the EU to bleed down to 60 V (thanks Martin Bonner!) within one second or you will get nasty shocks from the plug if you toutch it once unplugged. There are special X-rated capacitors with this resistor built-in. This is called a bleeder resistor. There is a tradeoff between time and power dissipation when plugged in so make sure you have sufficient voltage and power rating on it.

Your suggestion of aluminium foil wrapping won't do crap here due to too low frequency and conducted emission as opposed to radiated emission, where alumimium foil might have worked.

If you don't want to dissassemble your device, at low frequencies there is a fairly low penalty in placing the filer down the cable instead. Probably measureable, but managable.