Latest Nintendont, updated from Nintendont itself. Tried another USB and SD card, no difference. At this point is must be the iso since you're telling me that this game should work fine. I'm redumping it.

Latest Nintendont, updated from Nintendont itself. Tried another USB and SD card, no difference. At this point is must be the iso since you're telling me that this game should work fine. I'm redumping it.
why havent you checked your iso md5 yet?Just tried from multiple usb hdd / pen drives and new iso, nothing changed. I'm starting to think that it's not a problem with my configuration. I'll try again with the PAL version of the game.
Nintendont version is 3.326.

Hmm... Many people complain about Luigi's Mansion, what is it about that game that makes it cause a lot of issues? It seems to work fine on my end, NTSC version here, compressed iso, running from USB with Nintendont r320, I didn't play it all the way for a while but I'm playing for like half an hour now and didn't notice any issues!
the title screen appears but without music for the first 4-5 seconds; these 4-5 seconds of music are completely cut off (just like if you listen to a song from 0:04 instead of 0:00).
Thats totally normal, the very first load luigis mansion does basically loads up the entire game in a single go, not every device can load fast enough. It works fine the second time because as I said the game basically did a one time massive load.
. . . I used an uncompressed ISO ripped from my legit Nintendo disc running from a FAT32 SD card.

That's the key, IMHO. SD cards work so much better than USB drives. At least in my experience. Faster read & transfer rates, no need for external power source, and no stick protruding from the back or front. I invested in a 256GB SD card. Been flawless since.

Exact opposite for me.
My usb drive works MUCH faster than my sd card.

When I used a normal SD card, I got the same result, but when I use an EP SD card, it loads like lightning!
I paid 1/3 of the price for a 32gb usb key.
Sandisk Cruzers are bombs.

Huh... they don't work for me at all. They immediately freeze.
Exact opposite for me.
My usb drive works MUCH faster than my sd card.
When I used a normal SD card, I got the same result, but when I use an EP SD card, it loads like lightning!

Glad that works for you! I had bad experiences with mini sd cards. The adpaters slowed it down so much. Games would freeze mid play. I got THIS. But I paid $70 for it back then.
Adapters shouldn't slow microsd cards down at all . . . Most likely, you just got a bad microSD card or a broken adapter.
