That sounds terrible, 20 thou on a 4 in cutter. I would be looking for a thou or less on a new one. Must mearsure some of mine. When I hear it obviously not true I assume it is my arbor, collet, spindle.

With the radial runouts mentioned by the OP, only a few teeth will ever do any cutting.

Thay may come in useful once you have worn the first few down😉

Sorry but runout is down to your arbor, I have several and the only ones which are right are taper fit and cost decent money.

I have a large-ish selection of slitting saws made by various old school Sheffield manufacturers and they all, without exception, exhibit the pulsing sound when cutting which seems to suggest run-out even when running on my home made taper fitted arbors with imperceptible run-out.  I would have thought any half decent grinding machine would result in an undetectable difference in tooth grind.  Bandsaw blades are available with all sorts of tooth variations – skip tooth and variable tooth pitch to improve their cutting ability so it occurs to me that slitting saws may be designed to have a variable cutting action…

Rod