As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
STRONG ODOR OF PLASTIC WITH BOTH BLEEDS SELECTED ON. REMOVED AND REPLACED HEAT EXCHANGER P/N 778683-2, S/N OFF 840241, S/N ON 960411 IAW 21-50-05. REMOVED AND REPLACED ACM IAW W/C 21-50-03R. OPS AND LEAK CHECKS GOOD. 16APR07 - APU MAKES LOUD NOISE. MEL AUXILIARY POWER UNIT.