Shruti-1 - 4Pole MkII 200 Hz Hum

I finished my Shruti-1 with the 4Pole MkII and all seems to work.
However, every note I play has a 200 Hz hum included in the output.
When not triggered the output is dead quiet.
Any ideas on where to look?

Which power supply do you use?

A simple power brick, 9V DC, but will try battery to see if PS is the problem

The question is how much current it does provide. If it is too low, you’ll get some motorboating…

Also, is that a standard kit or have you used your own parts?

This is the standard kit. How much current should the PS supply?

About 150mA but some PSUs marked 300mA start failing at 150mA…

Just got me a better PSU, all motorboating is gone now! Thanks!