Hmm... the sound system in the T21 is an old Cirrus Logic? Let's see now... according to the ThinkPad Specifications Reference
website it's a... Cirrus Logic CS4624.
I remember my old ThinkPad 600e (which had another Cirrus Logic sound system, the CS4232). It was troublesome, but back then I didn't use PCLinuxOS (another distro with a funny-colored hat?). I seem to remember knocking around in the driver a bit... let me check my old notes.... nope, that's too far back.
Aha... looks like this is an AC'97 device? Here's a link to the datasheet for the CS4264
You might try playing around with the headphone volume slider and see if that acts as your actual master volume control. If so, there's a parameter you need to pass the driver. I do have some notes about that... (I forget where I found this originally... line number at left are from the original source)
2050 AC97 Quirk Option
2053 The ac97_quirk option is used to enable/override the workaround for
2054 specific devices on drivers for on-board AC'97 controllers like
2055 snd-intel8x0. Some hardware have swapped output pins between Master
2056 and Headphone, or Surround (thanks to confusion of AC'97
2057 specifications from version to version :-)
2059 The driver provides the auto-detection of known problematic devices,
2060 but some might be unknown or wrongly detected. In such a case, pass
2061 the proper value with this option.
2063 The following strings are accepted:
2064 - default Don't override the default setting
2065 - none Disable the quirk
2066 - hp_only Bind Master and Headphone controls as a single control
2067 - swap_hp Swap headphone and master controls
2068 - swap_surround Swap master and surround controls
2069 - ad_sharing For AD1985, turn on OMS bit and use headphone
2070 - alc_jack For ALC65x, turn on the jack sense mode
2071 - inv_eapd Inverted EAPD implementation
2072 - mute_led Bind EAPD bit for turning on/off mute LED
2074 For backward compatibility, the corresponding integer value -1, 0,
2075 ... are accepted, too.
2077 For example, if "Master" volume control has no effect on your device
2078 but only "Headphone" does, pass ac97_quirk=hp_only module option.
Give that a try. You'll probably need to open PCC and get in the Options dialog of your sound card's driver configuration to pass these parameters to it.
Jot back and let's see if we can get that old anti-quey