Not entirely related to MCE events, but apparently there's a whole lot of undiscovered ambient sounds, at least from this list. I have been living under a rock for a while though, so this might already be common knowledge by now.

Example: Ambient sound #200 plays the "oh thank you" sound from the ending, as long as there is ambient sound #33 somewhere else in the level.

#	Official Sound Name	Length (s)	Anim
0	sWIND_WIND2A	9.775	(107)
1	sCOMMON_BURNIN	1.086	(22)
2	sSCIENCE_PLOPKAOS	4.191	(78)
3	sAMMO_BMP2	0.139	(0)
4	sAMMO_BMP3	0.13	(0)
5	sAMMO_BMP4	0.117	(0)
6	sAMMO_BMP5	0.107	(0)
7	sAMMO_BMP6	0.27	(0)
8	sAMMO_BOEM1	0.596	(0)
9	sAMMO_BUL1	0.064	(0)
10	sAMMO_BULFL1	0.322	(0)
11	sAMMO_BULFL2	0.168	(0)
12	sAMMO_BULFL3	0.286	(0)
13	sAMMO_FIREGUN1A	0.708	(0)
14	sAMMO_FIREGUN2A	0.685	(0)
15	sAMMO_FUMP	0.07	(0)
16	sAMMO_GUN1	0.164	(0)
17	sAMMO_GUN2	0.183	(0)
18	sAMMO_GUN3PLOP	0.192	(0)
19	sAMMO_GUNFLP	0.069	(0)
20	sAMMO_GUNFLP1	0.075	(0)
21	sAMMO_GUNFLP2	0.069	(0)
22	sAMMO_GUNFLP3	0.058	(0)
23	sAMMO_GUNFLP4	0.047	(0)
24	sAMMO_GUNFLPL	0.052	(0)
25	sAMMO_GUNJAZZ	0.06	(0)
26	sAMMO_GUNVELOCITY	0.376	(0)
27	sAMMO_ICEGUN	0.181	(0)
28	sAMMO_ICEGUN2	0.151	(0)
29	sAMMO_ICEGUNPU	0.159	(0)
30	sAMMO_ICEPU1	0.227	(0)
31	sAMMO_ICEPU2	0.262	(0)
32	sAMMO_ICEPU3	0.254	(0)
33	sAMMO_ICEPU4	0.244	(0)
34	sAMMO_LASER	0.238	(0)
35	sAMMO_LASER2	0.67	(0)
36	sAMMO_LASER3	0.727	(0)
37	sAMMO_LAZRAYS	0.364	(0)
38	sAMMO_MISSILE	0.856	(0)
39	sAMMO_SPZBL1	0.237	(0)
40	sAMMO_SPZBL2	0.258	(0)
41	sAMMO_SPZBL3	0.205	(0)
42	sBAT_BATFLY1	0.644	1
43	sBILSBOSS_BILLAPPEAR	0.908	7
44	sBILSBOSS_FINGERSNAP	0.383	7
45	sBILSBOSS_FIRE	0.911	7
46	sBILSBOSS_FIRESTART	2.31	7
47	sBILSBOSS_SCARY3	8.828	7
48	sBILSBOSS_THUNDER	4.151	7
49	sBILSBOSS_ZIP	0.197	7
50	sBONUS_BONUS1	0.501	11
51	sBONUS_BONUSBLUB	1.149	11
52	sBUBBA_BUBBABOUNCE1	0.293	14
53	sBUBBA_BUBBABOUNCE2	0.253	14
54	sBUBBA_BUBBAEXPLO	0.977	14
55	sBUBBA_FROG2	0.148	14
56	sBUBBA_FROG3	0.16	14
57	sBUBBA_FROG4	0.191	14
58	sBUBBA_FROG5	0.147	14
59	sBUBBA_SNEEZE2	0.705	14
60	sBUBBA_TORNADOATTACK2	2.781	14
61	sBUMBEE_BEELOOP	3.037	15
62	sCATERPIL_RIDOE	2.017	20
63	sCOMMON_AIRBOARD	2.488	(22)
64	sCOMMON_AIRBTURN	0.135	(22)
65	sCOMMON_AIRBTURN2	0.067	(22)
66	sCOMMON_BASE1	0.34	(22)
67	sCOMMON_BELL_FIRE	0.375	(22)
68	sCOMMON_BELL_FIRE2	0.186	(22)
69	sCOMMON_BENZIN1	0.827	(22)
70	sCOMMON_BIRDFLY	0.425	(22)
71	sCOMMON_BIRDFLY2	0.421	(22)
72	sCOMMON_BLOKPLOP	0.046	(22)
73	sCOMMON_BLUB1	0.071	(22)
74	sCOMMON_BUBBLGN1	0.853	(22)
75	sCOMMON_BURN	0.988	(22)
76	sCOMMON_BURNIN	1.086	(22)
77	sCOMMON_CANSPS	0.638	(22)
78	sCOMMON_CLOCK	0.2	(22)
79	sCOMMON_COIN	0.354	(22)
80	sCOMMON_COLLAPS	0.866	(22)
81	sCOMMON_CUP	0.208	(22)
82	sCOMMON_DAMPED1	0.703	(22)
83	sCOMMON_DOWN	0.137	(22)
84	sCOMMON_DOWNFL2	0.366	(22)
85	sCOMMON_DRINKSPAZZ1	0.367	(22)
86	sCOMMON_DRINKSPAZZ2	0.28	(22)
87	sCOMMON_DRINKSPAZZ3	0.282	(22)
88	sCOMMON_DRINKSPAZZ4	0.367	(22)
89	sCOMMON_EAT1	0.582	(22)
90	sCOMMON_EAT2	0.305	(22)
91	sCOMMON_EAT3	0.238	(22)
92	sCOMMON_EAT4	0.277	(22)
93	sCOMMON_ELECTRIC1	0.507	(22)
94	sCOMMON_ELECTRIC2	0.872	(22)
95	sCOMMON_ELECTRICHIT	0.247	(22)
96	sCOMMON_EXPL_TNT	0.437	(22)
97	sCOMMON_EXPSM1	0.4	(22)
98	sCOMMON_FLAMER	0.817	(22)
99	sCOMMON_FLAP	0.552	(22)
100	sCOMMON_FOEW1	0.063	(22)
101	sCOMMON_FOEW2	0.14	(22)
102	sCOMMON_FOEW3	0.059	(22)
103	sCOMMON_FOEW4	0.067	(22)
104	sCOMMON_FOEW5	0.066	(22)
105	sCOMMON_GEMSMSH1	1.203	(22)
106	sCOMMON_GLASS2	1.229	(22)
107	sCOMMON_GUNSM1	0.332	(22)
108	sCOMMON_HARP1	1.19	(22)
109	sCOMMON_HEAD	0.897	(22)
110	sCOMMON_HELI1	0.422	(22)
111	sCOMMON_HIBELL	0.366	(22)
112	sCOMMON_HOLYFLUT	1.309	(22)
113	sCOMMON_HORN1	0.28	(22)
114	sCOMMON_ICECRUSH	0.644	(22)
115	sCOMMON_IMPACT1	0.3	(22)
116	sCOMMON_IMPACT2	0.296	(22)
117	sCOMMON_IMPACT3	0.242	(22)
118	sCOMMON_IMPACT4	0.148	(22)
119	sCOMMON_IMPACT5	0.218	(22)
120	sCOMMON_IMPACT6	0.413	(22)
121	sCOMMON_IMPACT7	0.378	(22)
122	sCOMMON_IMPACT8	0.337	(22)
123	sCOMMON_IMPACT9	0.179	(22)
124	sCOMMON_ITEMTRE	0.464	(22)
125	sCOMMON_JUMP	0.112	(22)
126	sCOMMON_JUMP2	0.314	(22)
127	sCOMMON_LAND	0.691	(22)
128	sCOMMON_LAND1	0.23	(22)
129	sCOMMON_LAND2	0.43	(22)
130	sCOMMON_LANDCAN1	0.162	(22)
131	sCOMMON_LANDCAN2	0.228	(22)
132	sCOMMON_LANDPOP	0.075	(22)
133	sCOMMON_LOADJAZZ	0.155	(22)
134	sCOMMON_LOADSPAZ	0.237	(22)
135	sCOMMON_METALHIT	0.386	(22)
136	sCOMMON_MONITOR	0.321	(22)
137	sCOMMON_NOCOIN	1.272	(22)
138	sCOMMON_PICKUP1	0.286	(22)
139	sCOMMON_PICKUPW1	0.348	(22)
140	sCOMMON_PISTOL1	0.475	(22)
141	sCOMMON_PLOOP1	0.542	(22)
142	sCOMMON_PLOP1	0.295	(22)
143	sCOMMON_PLOP2	0.187	(22)
144	sCOMMON_PLOP3	0.097	(22)
145	sCOMMON_PLOP4	0.068	(22)
146	sCOMMON_PLOPKORK	0.332	(22)
147	sCOMMON_PREEXPL1	0.196	(22)
148	sCOMMON_PREHELI	0.377	(22)
149	sCOMMON_REVUP	1.092	(22)
150	sCOMMON_RINGGUN	0.325	(22)
151	sCOMMON_RINGGUN2	0.718	(22)
152	sCOMMON_SHIELD1	0.865	(22)
153	sCOMMON_SHIELD4	1.212	(22)
154	sCOMMON_SHIELD_ELEC	0.91	(22)
155	sCOMMON_SHLDOF3	0.573	(22)
156	sCOMMON_SLIP	1.054	(22)
157	sCOMMON_SMASH	0.639	(22)
158	sCOMMON_SPLAT1	0.621	(22)
159	sCOMMON_SPLAT2	0.391	(22)
160	sCOMMON_SPLAT3	0.557	(22)
161	sCOMMON_SPLAT4	0.718	(22)
162	sCOMMON_SPLUT	0.356	(22)
163	sCOMMON_SPRING1	1.08	(22)
164	sCOMMON_STEAM	1.138	(22)
165	sCOMMON_STEP	0.098	(22)
166	sCOMMON_STRETCH	0.133	(22)
167	sCOMMON_SWISH1	0.27	(22)
168	sCOMMON_SWISH2	0.276	(22)
169	sCOMMON_SWISH3	0.662	(22)
170	sCOMMON_SWISH4	0.186	(22)
171	sCOMMON_SWISH5	0.177	(22)
172	sCOMMON_SWISH6	0.115	(22)
173	sCOMMON_SWISH7	0.149	(22)
174	sCOMMON_SWISH8	0.278	(22)
175	sCOMMON_TELPORT1	0.422	(22)
176	sCOMMON_TELPORT2	0.691	(22)
177	sCOMMON_UP	0.137	(22)
178	sCOMMON_WATER	0.401	(22)
179	sCOMMON_WOOD1	0.345	(22)
180	sDEMON_RUN	0.312	24
181	sDEVILDEVAN_DRAGONFIRE	1.559	27
182	sDEVILDEVAN_FLAP	0.524	27
183	sDEVILDEVAN_FROG4	0.191	27
184	sDEVILDEVAN_JUMPUP	0.113	27
185	sDEVILDEVAN_LAUGH	1.184	27
186	sDEVILDEVAN_PHASER2	0.499	27
187	sDEVILDEVAN_STRECH2	0.334	27
188	sDEVILDEVAN_STRECHTAIL	0.821	27
189	sDEVILDEVAN_STRETCH1	0.314	27
190	sDEVILDEVAN_STRETCH3	0.891	27
191	sDEVILDEVAN_VANISH1	1.687	27
192	sDEVILDEVAN_WHISTLEDESCENDING2	1.372	27
193	sDEVILDEVAN_WINGSOUT	1.62	27
194	sDOG_AGRESSIV	1.178	29
195	sDOG_SNIF1	0.34	29
196	sDOG_WAF1	0.26	29
197	sDOG_WAF2	0.269	29
198	sDOG_WAF3	0.221	29
199	sDRAGFLY_BEELOOP	3.037	31
200	sENDING_OHTHANK	3.096	33
201	sENDTUNEJAZZ_TUNE	5.457	34
202	sENDTUNESPAZ_TUNE	5.457	35
203	sEPICLOGO_EPIC1	7.291	36
204	sEPICLOGO_EPIC2	4.435	36
205	sEVA_KISS1	0.165	37
206	sEVA_KISS2	0.797	37
207	sEVA_KISS3	0.415	37
208	sEVA_KISS4	0.072	37
209	sFAN_FAN	0.821	39
210	sFATCHK_HIT1	0.409	40
211	sFATCHK_HIT2	0.464	40
212	sFATCHK_HIT3	0.158	40
213	sFENCER_FENCE1	0.296	41
214	sFROG_FROG	0.33	46
215	sFROG_FROG1	0.19	46
216	sFROG_FROG2	0.148	46
217	sFROG_FROG3	0.16	46
218	sFROG_FROG4	0.191	46
219	sFROG_FROG5	0.147	46
220	sFROG_JAZZ2FROG	1.585	46
221	sFROG_TONG	0.444	46
222	sGLOVE_HIT	0.237	49
223	sHATTER_CUP	0.093	51
224	sHATTER_HAT	0.164	51
225	sHATTER_PTOEI	0.345	51
226	sHATTER_SPLIN	0.464	51
227	sHATTER_SPLOUT	0.61	51
228	sINTRO_BLOW	0.34	53
229	sINTRO_BOEM1	2.392	53
230	sINTRO_BOEM2	1.763	53
231	sINTRO_BRAKE	1.29	53
232	sINTRO_END	0.75	53
233	sINTRO_GRAB	0.964	53
234	sINTRO_GREN1	1.669	53
235	sINTRO_GREN2	0.822	53
236	sINTRO_GREN3	0.831	53
237	sINTRO_GUNM0	0.76	53
238	sINTRO_GUNM1	0.546	53
239	sINTRO_GUNM2	0.555	53
240	sINTRO_HELI	3.448	53
241	sINTRO_HITSPAZ	0.325	53
242	sINTRO_HITTURT	0.316	53
243	sINTRO_IFEEL	1.678	53
244	sINTRO_INHALE	0.175	53
245	sINTRO_INSECT	2.874	53
246	sINTRO_KATROL	1.271	53
247	sINTRO_LAND	0.949	53
248	sINTRO_MONSTER	2.257	53
249	sINTRO_MONSTER2	0.543	53
250	sINTRO_ROCK	1.189	53
251	sINTRO_ROPE1	0.825	53
252	sINTRO_ROPE2	1.146	53
253	sINTRO_RUN	1.005	53
254	sINTRO_SHOT1	0.753	53
255	sINTRO_SHOTGRN	1.202	53

The Anim column indicates which extra anim needs to be loaded (i.e. another ambient sound), if it's parenthesised means it's already loaded. Also, this is for v1.23, so #110 and #111 will cause a crash.