Those might be very slight guitar overtones.
If you incorrectly fret a note on the guitar you may accidently catch a certain harmonic overtone that sounds like a 'pling'. It could be the way that that album was recorded too, maybe Mike and Pete were standing very close to the microphones on the amps so their fretting actions on the guitar were picked up by the microphones... thus resorting in little metal clinging sounds.
These theories could go for the bass as well...
All I know for sure is that the springy noise in 'Face Of Melinda' is Martin moving his index finger off the bass string.
Man, we are such nitpickers!