sideburns,
a solenoid should not 'buzz'... if it is, it is 'ready to fail'... if it is 'buzzing', the coil is not strong enough to lock it into position, so the actuator is vibrating back and forth. it is not 'locking' into the 'on' position, so it keeps trying... (could be the 'gumming up' one mentioned, or a piece of debris blocking the valve.)
electromagnets do not 'get weak'. they work, or they fail, but if the channel for the actuator is 'gummy' or partailly blocked... i recommend you do a flush and filter (and magnet) change, and soon. pull the pan to do so, but you should look into running some solvent in the tranny for a few minutes first, something similar to 'motor flush', which i use before i change my oil and filter.
btw, guys...
the newer solenoid pack was introduced in 1999, per the dealer, and will retrofit to older transmissions... new design, same function... the differences are...
the 'spacer plate' between the solenoid pack and the tranny is discarded, so only one gasket is needed, not two...
it IS a different gasket...
i assume that the new one is cheaper to produce, and therefore may not be as high a quality unit as the old one. the new gasket is a different cutout, to match the new channels in the new unit (and the new transmissions, i suppose) to the channels in the old transmission.
there are 'placement pins' (as others earlier have said) on the solenoid pack which position it on the tranny. the older solenoid pack 'pins' pass through both gaskets and the spacer... since the spacer is not used when retrofitting, i would bet those pins are shorter...
regards...
dnorm