96Aurora 4t80E trans

Recently replaced A and B solinoids with Delco Kit per Sweet William instructions. This fixed my 2-3 shift problem. Since the new solinoids were installed I get a very quiet buzzing sound in 2nd gear just before the 2-3 shift. It only does it when the engine and tranny are cold, it doesn't do it after the engine and tranny are up to full operationg temp. If I hold a steady 29 mph just before the 2-3 shift the buzz sound persists, when I accelerate up to over 30 MPH it makes the 2-3 shift and the buzz goes away, 3-4 shift works fine. Got me puzzled, Help????

Found the answer today, Took lower control valve out and disassembled, found that the gasket on the accumulator housing cover had blown out, hard to see, made new gasket, now it shifts perfect and no more buzz. Note: every transmission shop including the stealer said I needed a new tranny at prices from 1900 to 2800. Pays to "Know"