Weird lowrider "problem" (includes solution ... but not understanding)

[midwayfair]

I was getting some squeal in a lowrider I just built originating at 6&7 of IC5B. It appeared on the pins, but if I touched the junction of R33/R32 it went away. I started poking around a bit and experimenting and I found I could make it go away with about 33pF of capacitance across IC33, or by shunting the same amount to ground, or adding some capacitance to C21 (but that took more). It still squeals a tiny bit on power up for about 2-3 seconds (obviously only if the second octave down pot is turned up at all). I went and grabbed my old lowrider and noticed that it had a little "peep" on power up, but it didn't last as long, maybe a quarter of a second.

Increasing the capacitance strapped across R33 decreased the amount of time the squeal was audible, but it also cut the volume of the second octave down. I ended up using 150pF, which resulted in perhaps a 1 second squeal with minimal volume loss (which I didn't care about too much ... I boosted R52 on this one anyway so that the whole effect has more output now).

Nothing is wrong with the effect -- it works just fine, tracking is just as good as ever, no magic smoke, etc.

Could anyone venture a guess as to what is (a) causing the squeal (I've swapped the 074 with no change - so it's not a bad op amp) and (b) if perhaps a part went bad that I didn't think of?

[midwayfair]

Bump for thoughts?