Boss Bf-2 Flanger Noisy!!

[Rob Strand]

Which other resistors in the signal path do you consider are critical for changing to metal film for noise reduction?

Changing the resistor type is just crazy.  You would be lucky to measure the change in noise never mind hear it.

The dominant source of noise is the BBD device.   You can't change that.  The circuit already uses a good amount of pre-emphasis and de-emphasis so you aren't going to gain much there either.  Where you will gain is filtering more high frequencies out by decreasing the filter cut-off of the filter IC2A (pin 1,2,3).  The side-effect is it will change the sound a bit.

(Resistors R7 and R13 are adding noise unnecessarily but the added noise is well under the radar compare to the BBD.)

[Rob Strand]

As an experiment you could try this:  Double the value of C18 (1n) and C19 (150p), so C18 is 2n2 and C19 is 330p.  Alternatively, to try it,  you could solder a 1n cap on the back of C18 and a 150pF cap on the back of C19.  You can further experiment by using a factor different than 2 eg. 1.5 for less filtering and 3.0 for more.
Anyway I hope you get the idea.   You are trading noise removal for loss of treble (but only on the delayed signal, the clean signal is left alone.)