Strange audio problem with Messiah 2 chip

[IVAHOTROD]

i have a messiah 2 chipped ps2 (v30003R), im encountering some weird audio problems, for example; sometimes at bootup the sony booting sound is echoing badly (like your tripping!!) then if i reboot and its ok, later in a game the same thing happens, the sound goes all tinny and echo's badly, or sometimes the background sound dissappears altogether and comes back again. I have tried pot adjustment (no, not the dope kind) with limited success. could the fault be with the messiah 2 or is the laser Fecked or the ps2 itself ?

im using Techno brand dvd-r which work fine on all other ps2's i have tried.

hope someone can shed a little light on this one